Optionalise kerberos, cups, NetworkManager, bluetooth, wacom and GOA; replace absolute paths.
Rebased for 51.0 from the ::gentoo (pacho) 50.4 patchset 0001-0005, merged into one patch.

diff -ruN a/meson.build b/meson.build
--- a/meson.build
+++ b/meson.build
@@ -232,7 +232,7 @@
 gnome_bg_dep = dependency('gnome-bg-4')
 gnome_qr_gtk_dep = dependency('gnome-qr-gtk-4')
 gnome_settings_dep = dependency('gnome-settings-daemon', version: '>= 48.rc', fallback: 'gsd')
-goa_dep = dependency('goa-1.0', version: goa_req_version, fallback: 'goa')
+goa_dep = dependency('goa-1.0', version: goa_req_version, required: get_option('goa'))
 gsettings_desktop_dep = dependency('gsettings-desktop-schemas', version: '>= 51.beta')
 libxml_dep = dependency('libxml-2.0')
 pulse_dep = dependency('libpulse', version: pulse_req_version)
@@ -245,6 +245,10 @@
 
 m_dep = cc.find_library('m')
 
+enable_goa = goa_dep.found()
+config_h.set('BUILD_GOA', enable_goa,
+             description: 'Define to 1 to build the Online Accounts panel')
+
 common_deps = [
   gio_dep,
   glib_dep,
@@ -270,29 +274,35 @@
                description: 'Define if langinfo.h supports _NL_TIME_FIRST_WEEKDAY')
 endif
 
-# Check for CUPS 1.4 or newer
-cups_dep = dependency('cups', version : '>= 1.4', required: false)
-assert(cups_dep.found(), 'CUPS 1.4 or newer not found')
-
-# https://bugzilla.gnome.org/show_bug.cgi?id=696766
-cups_cflags = []
-if cups_dep.version().version_compare('>= 1.6')
-  cups_cflags += '-D_PPD_DEPRECATED='
-endif
-
-# cups headers
-check_headers = [
-  ['HAVE_CUPS_CUPS_H', 'cups/cups.h'],
-  ['HAVE_CUPS_PPD_H', 'cups/ppd.h']
-]
-
-foreach header: check_headers
-  assert(cc.has_header(header[1], args: cups_cflags), 'CUPS headers not found: ' + header[1])
-endforeach
+# Optional dependency for the printers panel
+enable_cups = get_option('cups')
+if enable_cups
+  # Check for CUPS 1.4 or newer
+  cups_dep = dependency('cups', version : '>= 1.4', required: false)
+  assert(cups_dep.found(), 'CUPS 1.4 or newer not found')
+
+  # https://bugzilla.gnome.org/show_bug.cgi?id=696766
+  cups_cflags = []
+  if cups_dep.version().version_compare('>= 1.6')
+    cups_cflags += '-D_PPD_DEPRECATED='
+  endif
+
+  # cups headers
+  check_headers = [
+    ['HAVE_CUPS_CUPS_H', 'cups/cups.h'],
+    ['HAVE_CUPS_PPD_H', 'cups/ppd.h']
+  ]
 
-config_h.set10('HAVE_CUPS_HTTPCONNECT2',
-               cc.has_function('httpConnect2', dependencies: cups_dep),
-               description: 'Define if httpConnect2() is available in CUPS')
+  foreach header: check_headers
+    assert(cc.has_header(header[1], args: cups_cflags), 'CUPS headers not found: ' + header[1])
+  endforeach
+
+  config_h.set10('HAVE_CUPS_HTTPCONNECT2',
+                 cc.has_function('httpConnect2', dependencies: cups_dep),
+                 description: 'Define if httpConnect2() is available in CUPS')
+endif
+config_h.set('HAVE_CUPS', enable_cups,
+             description: 'Defined if cups support is enabled')
 
 
 # IBus support
@@ -303,6 +313,16 @@
 config_h.set('HAVE_IBUS', enable_ibus,
              description: 'Defined if IBus support is enabled')
 
+# Kerberos support
+enable_kerberos = get_option('kerberos')
+if enable_kerberos
+    kerberos_deps = [
+      dependency('krb5')
+    ]
+endif
+config_h.set('HAVE_KERBEROS', enable_kerberos,
+             description: 'Defined if kerberos support is enabled')
+
 # thunderbolt
 config_h.set10('HAVE_FN_EXPLICIT_BZERO',
                cc.has_function('explicit_bzero', prefix: '''#include <string.h>'''),
@@ -347,7 +367,8 @@
 config_h.set('HAVE_SSH_SOCKET_ACTIVATION', ssh_socket_activation,
              description: 'Whether SSH socket activation is enabled')
 
-if host_is_linux
+enable_network_manager = get_option('network_manager')
+if enable_network_manager
   # ModemManager
   mm_dep =  dependency('mm-glib', version: '>= 0.7')
   # NetworkManager
@@ -358,35 +379,42 @@
     mm_dep,
   ]
 endif
-config_h.set('BUILD_NETWORK', host_is_linux,
+config_h.set('BUILD_NETWORK', enable_network_manager,
              description: 'Define to 1 to build the Network panel')
-config_h.set('HAVE_NETWORK_MANAGER', host_is_linux,
+config_h.set('HAVE_NETWORK_MANAGER', enable_network_manager,
              description: 'Define to 1 if NetworkManager is available')
-config_h.set('BUILD_WWAN', host_is_linux,
+config_h.set('BUILD_WWAN', enable_network_manager,
              description: 'Define to 1 to build the WWan panel')
-config_h.set('HAVE_WWAN', host_is_linux,
+config_h.set('HAVE_WWAN', enable_network_manager,
              description: 'Define to 1 if WWan is available')
 
-if host_is_linux_not_s390
+enable_bluetooth = get_option('bluetooth')
+if enable_bluetooth
   # gnome-bluetooth
   gnome_bluetooth_dep = dependency('gnome-bluetooth-ui-3.0')
+endif
 
+enable_wacom = get_option('wacom')
+if enable_wacom
+  # Wacom
   libwacom_dep = dependency('libwacom', version: '>= 1.4')
 
   wacom_deps = [
     libwacom_dep,
   ]
-else
-  message('Bluetooth and Wacom panels will not be built (no USB support on this platform)')
+endif
+
+if not host_is_linux_not_s390
   message('Thunderbolt panel will not be built (not supported on this platform)')
 endif
-config_h.set('BUILD_BLUETOOTH', host_is_linux_not_s390,
+
+config_h.set('BUILD_BLUETOOTH', enable_bluetooth,
              description: 'Define to 1 to build the Bluetooth panel')
-config_h.set('HAVE_BLUETOOTH', host_is_linux_not_s390,
+config_h.set('HAVE_BLUETOOTH', enable_bluetooth,
              description: 'Define to 1 if bluetooth support is available')
-config_h.set('BUILD_WACOM', host_is_linux_not_s390,
+config_h.set('BUILD_WACOM', enable_wacom,
              description: 'Define to 1 to build the Wacom panel')
-config_h.set('HAVE_WACOM', host_is_linux_not_s390,
+config_h.set('HAVE_WACOM', enable_wacom,
              description: 'Define to 1 if Wacom is supportted')
 config_h.set('BUILD_THUNDERBOLT', host_is_linux_not_s390,
              description: 'Define to 1 to build the Thunderbolt panel')
@@ -441,16 +469,18 @@
 )
 
 summary({
-    'GNOME Bluetooth': host_is_linux_not_s390,
-    'NetworkManager': host_is_linux,
-    'Wacom': host_is_linux_not_s390,
+    'GNOME Bluetooth': enable_bluetooth,
+    'NetworkManager': enable_network_manager,
+    'Wacom': enable_wacom,
   },
   section: 'Dependencies',
   bool_yn: true,
 )
 
 summary({
+    'Cups': enable_cups,
     'IBus': enable_ibus,
+    'Kerberos': enable_kerberos,
     'Snap': enable_snap,
     'Malcontent': enable_malcontent,
   },
diff -ruN a/meson_options.txt b/meson_options.txt
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -1,10 +1,16 @@
+option('bluetooth', type: 'boolean', value: true, description: 'build with Bluetooth support')
 option('deprecated-declarations', type: 'feature', value: 'disabled', description: 'build with deprecated declaration warnings')
+option('cups', type: 'boolean', value: true, description: 'build with cups support')
 option('documentation', type: 'boolean', value: false, description: 'build documentation')
 option('location-services', type: 'feature', value: 'enabled', description: 'build with location services')
+option('goa', type: 'feature', value: 'auto', description: 'build with gnome-online-accounts support')
 option('ibus', type: 'boolean', value: true, description: 'build with IBus support')
+option('network_manager', type: 'boolean', value: true, description: 'build with NetworkManager support')
+option('kerberos', type: 'boolean', value: true, description: 'build with kerberos support')
 option('privileged_group', type: 'string', value: 'wheel', description: 'name of group that has elevated permissions')
 option('snap', type: 'boolean', value: true, description: 'build with Snap support')
 option('tests', type: 'boolean', value: true, description: 'build tests')
+option('wacom', type: 'boolean', value: true, description: 'build with Wacom support')
 option('malcontent', type: 'boolean', value: false, description: 'build with malcontent support')
 option('ssh_socket_activation', type: 'boolean', value: false, description: 'build with SSH socket activation support')
 option('distributor_logo', type: 'string', description: 'absolute path to distributor logo for the About panel')
diff -ruN a/panels/applications/meson.build b/panels/applications/meson.build
--- a/panels/applications/meson.build
+++ b/panels/applications/meson.build
@@ -62,7 +62,7 @@
 
 deps = common_deps + [keyboard_shortcuts_dep]
 
-if host_is_linux
+if enable_network_manager
   deps += mm_dep
 endif
 
diff -ruN a/panels/meson.build b/panels/meson.build
--- a/panels/meson.build
+++ b/panels/meson.build
@@ -12,9 +12,7 @@
   'mouse',
   'multitasking',
   'notifications',
-  'online-accounts',
   'power',
-  'printers',
   'privacy',
   'search',
   'sharing',
@@ -22,18 +20,26 @@
   'system',
   'universal-access',
   'wellbeing',
-  'wwan',
 ]
 
-if host_is_linux
-  panels += ['network']
+if enable_cups
+  panels += ['printers']
 endif
 
-if host_is_linux_not_s390
-  panels += [
-    'bluetooth',
-    'wacom'
-  ]
+if enable_goa
+  panels += ['online-accounts']
+endif
+
+if enable_network_manager
+  panels += ['network', 'wwan']
+endif
+
+if enable_bluetooth
+  panels += [ 'bluetooth' ]
+endif
+
+if enable_wacom
+  panels += [ 'wacom' ]
 endif
 
 panels_list = []
diff -ruN a/panels/printers/meson.build b/panels/printers/meson.build
--- a/panels/printers/meson.build
+++ b/panels/printers/meson.build
@@ -76,6 +76,11 @@
   sources += 'pp-samba-stub.c'
 endif
 
+cflags += [
+  '-DDATADIR="@0@"'.format(control_center_datadir),
+  '-DLIBEXECDIR="@0@"'.format(control_center_libexecdir)
+]
+
 printers_panel_lib = static_library(
   cappletname,
   sources: sources,
diff -ruN a/panels/printers/pp-host.c b/panels/printers/pp-host.c
--- a/panels/printers/pp-host.c
+++ b/panels/printers/pp-host.c
@@ -214,7 +214,7 @@
     devices = g_ptr_array_new_with_free_func (g_object_unref);
 
     argv = g_new0 (gchar *, 3);
-    argv[0] = g_strdup ("/usr/lib/cups/backend/snmp");
+    argv[0] = g_strdup (LIBEXECDIR "/cups/backend/snmp");
     argv[1] = g_strdup (priv->hostname);
 
     /* Use SNMP to get printer's informations */
diff -ruN a/panels/printers/pp-options-dialog.c b/panels/printers/pp-options-dialog.c
--- a/panels/printers/pp-options-dialog.c
+++ b/panels/printers/pp-options-dialog.c
@@ -641,7 +641,7 @@
     gint i;
 
     if (self->printer_name) {
-        const gchar *const dirs[] = { "/usr/share/cups", "/usr/local/share/cups", NULL };
+        const gchar *const dirs[] = { DATADIR "/cups", "/usr/local/share/cups", NULL };
         const gchar *datadir = NULL;
         g_autofree gchar *filename = NULL;
 
diff -ruN a/panels/system/datetime/tz.h b/panels/system/datetime/tz.h
--- a/panels/system/datetime/tz.h
+++ b/panels/system/datetime/tz.h
@@ -28,9 +28,9 @@
 G_BEGIN_DECLS
 
 #ifndef __sun
-#define TZ_DATA_FILE "/usr/share/zoneinfo/zone.tab"
+#define TZ_DATA_FILE DATADIR "/zoneinfo/zone.tab"
 #else
-#define TZ_DATA_FILE "/usr/share/lib/zoneinfo/tab/zone_sun.tab"
+#define TZ_DATA_FILE DATADIR "/lib/zoneinfo/tab/zone_sun.tab"
 #endif
 
 typedef struct _TzDB TzDB;
diff -ruN a/panels/system/meson.build b/panels/system/meson.build
--- a/panels/system/meson.build
+++ b/panels/system/meson.build
@@ -91,8 +91,7 @@
 udisks2 = dependency('udisks2', version: '>= 2.8.2')
 
 # Kerberos support
-krb_dep = dependency('krb5', required: false)
-assert(krb_dep.found(), 'kerberos libraries not found in your path')
+krb_dep = dependency('krb5', required: enable_kerberos)
 
 deps = common_deps + [
   accounts_dep,
@@ -104,7 +103,6 @@
   libgtop2,
   liblanguage_dep,
   libsecret_dep,
-  krb_dep,
   polkit_gobject_dep,
   pwquality_dep,
   udisks2,
@@ -122,6 +120,10 @@
   deps += malcontent_dep
 endif
 
+if enable_kerberos
+  deps += krb_dep
+endif
+
 settings_daemon = 'org.gnome.SettingsDaemon'
 gsd_gdbus = settings_daemon + '.Sharing'
 
diff -ruN a/panels/system/users/cc-realm-manager.c b/panels/system/users/cc-realm-manager.c
--- a/panels/system/users/cc-realm-manager.c
+++ b/panels/system/users/cc-realm-manager.c
@@ -22,7 +22,9 @@
 
 #include "cc-realm-manager.h"
 
+#if defined(HAVE_KERBEROS)
 #include <krb5/krb5.h>
+#endif
 
 #include <glib.h>
 #include <glib/gi18n.h>
@@ -535,6 +537,7 @@
     g_slice_free (LoginClosure, login);
 }
 
+#if defined(HAVE_KERBEROS)
 static krb5_error_code
 login_perform_kinit (krb5_context k5, const gchar *realm, const gchar *login, const gchar *password,
                      const gchar *filename)
@@ -664,6 +667,7 @@
     if (k5)
         krb5_free_context (k5);
 }
+#endif
 
 void
 cc_realm_login (CcRealmObject *realm, const gchar *user, const gchar *password, GCancellable *cancellable,
@@ -692,7 +696,12 @@
     g_task_set_task_data (task, login, login_closure_free);
 
     g_task_set_return_on_cancel (task, TRUE);
+#if defined(HAVE_KERBEROS)
     g_task_run_in_thread (task, kinit_thread_func);
+#else
+        g_task_return_new_error (task, CC_REALM_ERROR, CC_REALM_ERROR_NOT_SUPPORTED,
+                                 _("kerberos based authentication support is disabled"));
+#endif
 }
 
 GBytes *
diff -ruN a/panels/system/users/cc-realm-manager.h b/panels/system/users/cc-realm-manager.h
--- a/panels/system/users/cc-realm-manager.h
+++ b/panels/system/users/cc-realm-manager.h
@@ -30,6 +30,7 @@
     CC_REALM_ERROR_CANNOT_AUTH,
     CC_REALM_ERROR_BAD_HOSTNAME,
     CC_REALM_ERROR_GENERIC,
+        CC_REALM_ERROR_NOT_SUPPORTED,
 } CcRealmErrors;
 
 #define CC_REALM_ERROR (cc_realm_error_get_quark ())
diff -ruN a/panels/system/users/meson.build b/panels/system/users/meson.build
--- a/panels/system/users/meson.build
+++ b/panels/system/users/meson.build
@@ -95,11 +95,11 @@
 )
 
 # Kerberos support
-krb_dep = dependency('krb5', required: false)
-assert(krb_dep.found(), 'kerberos libraries not found in your path')
+krb_dep = dependency('krb5', required: enable_kerberos)
 
 cflags += [
   '-DGNOMELOCALEDIR="@0@"'.format(control_center_localedir),
+  '-DBINDIR="@0@"'.format(control_center_bindir),
   '-DHAVE_LIBPWQUALITY',
   '-DUM_PIXMAP_DIR="@0@"'.format(join_paths(control_center_pkgdatadir, 'pixmaps'))
 ]
diff -ruN a/panels/system/users/run-passwd.c b/panels/system/users/run-passwd.c
--- a/panels/system/users/run-passwd.c
+++ b/panels/system/users/run-passwd.c
@@ -144,7 +144,7 @@
     gchar **envp;
     gint my_stdin, my_stdout;
 
-    argv[0] = "/usr/bin/passwd"; /* Is it safe to rely on a hard-coded path? */
+    argv[0] = BINDIR "/passwd";
     argv[1] = NULL;
 
     envp = g_get_environ ();
diff -ruN a/shell/cc-panel-loader.c b/shell/cc-panel-loader.c
--- a/shell/cc-panel-loader.c
+++ b/shell/cc-panel-loader.c
@@ -47,9 +47,13 @@
 extern GType cc_wifi_panel_get_type (void);
 #endif /* BUILD_NETWORK */
 extern GType cc_notifications_panel_get_type (void);
+#ifdef BUILD_GOA
 extern GType cc_online_accounts_panel_get_type (void);
+#endif /* BUILD_GOA */
 extern GType cc_power_panel_get_type (void);
+#ifdef HAVE_CUPS
 extern GType cc_printers_panel_get_type (void);
+#endif /* HAVE_CUPS */
 extern GType cc_privacy_panel_get_type (void);
 extern GType cc_search_panel_get_type (void);
 extern GType cc_sharing_panel_get_type (void);
@@ -100,9 +104,13 @@
     PANEL_TYPE ("wifi", cc_wifi_panel_get_type, cc_wifi_panel_static_init_func),
 #endif
     PANEL_TYPE ("notifications", cc_notifications_panel_get_type, NULL),
+#ifdef BUILD_GOA
     PANEL_TYPE ("online-accounts", cc_online_accounts_panel_get_type, NULL),
+#endif
     PANEL_TYPE ("power", cc_power_panel_get_type, NULL),
+#ifdef HAVE_CUPS
     PANEL_TYPE ("printers", cc_printers_panel_get_type, NULL),
+#endif
     PANEL_TYPE ("privacy", cc_privacy_panel_get_type, NULL),
     PANEL_TYPE ("search", cc_search_panel_get_type, NULL),
     PANEL_TYPE ("sharing", cc_sharing_panel_get_type, cc_sharing_panel_static_init_func),
diff -ruN a/shell/meson.build b/shell/meson.build
--- a/shell/meson.build
+++ b/shell/meson.build
@@ -120,7 +120,7 @@
   libshell_dep,
 ]
 
-if host_is_linux_not_s390
+if enable_wacom
   shell_deps += wacom_deps
 endif
 
diff -ruN a/tests/printers/meson.build b/tests/printers/meson.build
--- a/tests/printers/meson.build
+++ b/tests/printers/meson.build
@@ -1,22 +1,23 @@
 
-test_units = [
-  #'test-canonicalization',
-  'test-shift'
-]
+if enable_cups
+  test_units = [
+    #'test-canonicalization',
+    'test-shift'
+  ]
 
-includes = [top_inc, include_directories('../../panels/printers')]
-cflags = '-DTEST_SRCDIR="@0@"'.format(meson.current_source_dir())
+  includes = [top_inc, include_directories('../../panels/printers')]
+  cflags = '-DTEST_SRCDIR="@0@"'.format(meson.current_source_dir())
 
-foreach unit: test_units
-  exe = executable(
-                    unit,
-           [unit + '.c'],
-    include_directories : includes,
-           dependencies : common_deps,
-              link_with : [printers_panel_lib],
-                 c_args : cflags
-  )
-
-  test(unit, exe)
-endforeach
+  foreach unit: test_units
+    exe = executable(
+                      unit,
+             [unit + '.c'],
+      include_directories : includes,
+             dependencies : common_deps,
+                link_with : [printers_panel_lib],
+                   c_args : cflags
+    )
 
+    test(unit, exe)
+  endforeach
+endif