Upstream de-automagicked most optional dependencies in 0.7.x (cam-output-kms,
cam-output-sdl2, cam-jpeg, apps-output-dng, libdw), but IPA module signing via
gnutls is still auto-detected. Add a 'gnutls' feature option and honour it so
the openssl USE flag can deterministically select the crypto backend.

diff --git a/meson_options.txt b/meson_options.txt
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -66,7 +66,12 @@ option('apps-output-dng',
         type : 'feature',
         value : 'auto',
         description : 'Enable DNG file creation support in the cam and qcam applications')

+option('gnutls',
+        type : 'feature',
+        value : 'auto',
+        description : 'Compile libcamera with IPA module signing support using GNU TLS library')
+
 option('libunwind',
         type : 'feature',
         value : 'auto',
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -88,7 +88,7 @@ libudev = dependency('libudev', required : get_option('udev'))
 ])

 # Use one of gnutls or libcrypto (provided by OpenSSL), trying gnutls first.
-libcrypto = dependency('gnutls', required : false)
+libcrypto = dependency('gnutls', required : get_option('gnutls'))
 if libcrypto.found()
     config_h.set('HAVE_GNUTLS', 1)
 else