Build against Gentoo's system libraries instead of the upstream deps tree.

- Tracy: only the headers are needed with SLIC3R_ENABLE_PROFILING=OFF.
- wxGTK is built with autotools and ships no CMake config, use wx-config.
- Gentoo's zstd has no CMake config; a shared blosc does not need it.
- app-arch/libdeflate is only built as a shared library (libdeflate_shared).
- webkit2gtk-4.0 (libsoup2) must not be mixed with wxGTK's webkit2gtk-4.1.
- prusa-fdm-mixer is built from bundled_deps/ (unpacked by the ebuild).
- nlohmann_json 3.12.0 is used from bundled_deps/ with the std::optional fix
  and implicit conversions disabled, like upstream deps/+json. libslic3r
  includes it too but did not link the target.
- The glfw and SDL2 imgui backends are not linked by anything on Linux.

diff --git a/bundled_deps/CMakeLists.txt b/bundled_deps/CMakeLists.txt
index de8003c..6d6b7ee 100644
--- a/bundled_deps/CMakeLists.txt
+++ b/bundled_deps/CMakeLists.txt
@@ -10,6 +10,16 @@ add_subdirectory(hints)
 add_subdirectory(libnest2d)
 add_subdirectory(clipper)
 
+add_library(prusa_fdm_mixer STATIC prusa_fdm_mixer/prusa_fdm_mixer/prusa_fdm_mixer.cpp)
+add_library(prusa_fdm_mixer::prusa_fdm_mixer ALIAS prusa_fdm_mixer)
+target_include_directories(prusa_fdm_mixer PUBLIC prusa_fdm_mixer)
+
+# nlohmann_json 3.12.0 with the std::optional fix, configured like upstream deps/+json
+set(JSON_BuildTests OFF)
+set(JSON_ImplicitConversions OFF)
+set(JSON_Install OFF)
+add_subdirectory(nlohmann_json EXCLUDE_FROM_ALL)
+
 add_library(semver STATIC
     semver/semver.c
     semver/semver.h
diff --git a/bundled_deps/imgui/CMakeLists.txt b/bundled_deps/imgui/CMakeLists.txt
index b74eedb..3b5e2ca 100644
--- a/bundled_deps/imgui/CMakeLists.txt
+++ b/bundled_deps/imgui/CMakeLists.txt
@@ -23,6 +23,8 @@ target_include_directories(imgui PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
 message(STATUS "Imgui include dir: ${CMAKE_CURRENT_SOURCE_DIR}")
 
 
+# Gentoo: the glfw and SDL2 backends are not linked by any target on Linux
+if (NOT CMAKE_SYSTEM_NAME STREQUAL "Linux")
 add_library(imgui_backend_ogl3_glfw STATIC
         imgui/backends/imgui_impl_glfw.h
         imgui/backends/imgui_impl_glfw.cpp
@@ -72,6 +74,7 @@ target_link_libraries(
 if (APPLE)
     target_link_libraries(imgui_backend_ogl3_sdl2 PUBLIC "-framework Cocoa" "-framework IOKit")
 endif ()
+endif ()
 
 add_library(imgui_backend_ogl3 STATIC
         imgui/backends/imgui_impl_opengl3.h
diff --git a/cmake/modules/FindBlosc.cmake b/cmake/modules/FindBlosc.cmake
index 1c59ddd..44341a1 100644
--- a/cmake/modules/FindBlosc.cmake
+++ b/cmake/modules/FindBlosc.cmake
@@ -349,8 +349,11 @@ get_filename_component(Blosc_LIBRARY_DIRS ${Blosc_LIBRARY_RELEASE} DIRECTORY)
 
 if(NOT TARGET Blosc::blosc)
   add_library(Blosc::blosc ${BLOSC_LIB_TYPE} IMPORTED)
-  find_package(zstd REQUIRED)
-  target_link_libraries(Blosc::blosc INTERFACE zstd::libzstd)
+  # A shared libblosc already links zstd itself
+  if(BLOSC_LIB_TYPE STREQUAL "STATIC")
+    find_package(zstd REQUIRED)
+    target_link_libraries(Blosc::blosc INTERFACE zstd::libzstd)
+  endif()
   set_target_properties(Blosc::blosc PROPERTIES
     INTERFACE_COMPILE_OPTIONS "${PC_Blosc_CFLAGS_OTHER}"
     INTERFACE_INCLUDE_DIRECTORIES "${Blosc_INCLUDE_DIRS}")
diff --git a/cmake/modules/GlobalDependencies.cmake b/cmake/modules/GlobalDependencies.cmake
index c9f1cbe..5d17548 100644
--- a/cmake/modules/GlobalDependencies.cmake
+++ b/cmake/modules/GlobalDependencies.cmake
@@ -70,4 +70,11 @@ endif()
 find_package(fmt REQUIRED)
 slic3r_remap_configs(fmt::fmt RelWithDebInfo Release)
 
-find_package(Tracy REQUIRED)
+if (SLIC3R_ENABLE_PROFILING)
+    find_package(Tracy REQUIRED)
+else ()
+    # Only the (no-op) headers are needed when profiling is disabled.
+    find_path(TRACY_INCLUDE_DIR tracy/Tracy.hpp REQUIRED)
+    add_library(Tracy::TracyClient INTERFACE IMPORTED GLOBAL)
+    target_include_directories(Tracy::TracyClient INTERFACE ${TRACY_INCLUDE_DIR})
+endif ()
diff --git a/src/libslic3r/CMakeLists.txt b/src/libslic3r/CMakeLists.txt
index edb8f29..b9ce5fc 100644
--- a/src/libslic3r/CMakeLists.txt
+++ b/src/libslic3r/CMakeLists.txt
@@ -453,6 +453,7 @@ find_package(JPEG REQUIRED)
 
 target_link_libraries(libslic3r PRIVATE
     libexpat
+    nlohmann_json::nlohmann_json
     qhull
     TBB::tbb
     TBB::tbbmalloc
diff --git a/src/slic3r-biz-algorithms/CMakeLists.txt b/src/slic3r-biz-algorithms/CMakeLists.txt
index f0ddbf6..37cfd5d 100644
--- a/src/slic3r-biz-algorithms/CMakeLists.txt
+++ b/src/slic3r-biz-algorithms/CMakeLists.txt
@@ -115,7 +115,6 @@ else()
     target_link_libraries(qhull INTERFACE Qhull::qhullcpp Qhull::qhull_r)
 endif()
 
-find_package(prusa_fdm_mixer CONFIG REQUIRED)
 slic3r_remap_configs(prusa_fdm_mixer::prusa_fdm_mixer RelWithDebInfo Release)
 
 target_link_libraries(slic3r-biz-algorithms PRIVATE localesutils glu-libtess qhull prusa_fdm_mixer::prusa_fdm_mixer)
diff --git a/src/slic3r-platform-wx/CMakeLists.txt b/src/slic3r-platform-wx/CMakeLists.txt
index 38e7b6a..1d9a987 100644
--- a/src/slic3r-platform-wx/CMakeLists.txt
+++ b/src/slic3r-platform-wx/CMakeLists.txt
@@ -27,7 +27,7 @@ set(WX_COMPONENTS base core adv html gl)
 if(SLIC3R_ENABLE_WEBKIT)
     list(APPEND WX_COMPONENTS webview)
 endif()
-find_package(wxWidgets 3.3 CONFIG REQUIRED COMPONENTS ${WX_COMPONENTS})
+find_package(wxWidgets 3.3 REQUIRED COMPONENTS ${WX_COMPONENTS})
 
 slic3r_remap_configs(wx::wxhtml wx::wxadv wx::wxgl wx::wxcore wx::wxbase RelWithDebInfo Release)
 
diff --git a/src/slic3r-shared-wx/CMakeLists.txt b/src/slic3r-shared-wx/CMakeLists.txt
index 3c1682f..b0522ce 100644
--- a/src/slic3r-shared-wx/CMakeLists.txt
+++ b/src/slic3r-shared-wx/CMakeLists.txt
@@ -165,7 +165,7 @@ if (UNIX AND NOT APPLE)
 
     set(WEBKIT_LINK_LIBS "")
     if (SLIC3R_ENABLE_WEBKIT)
-        pkg_search_module(WEBKIT2GTK REQUIRED IMPORTED_TARGET webkit2gtk-4.0 webkit2gtk-4.1)
+        pkg_search_module(WEBKIT2GTK REQUIRED IMPORTED_TARGET webkit2gtk-4.1)
         set(WEBKIT_LINK_LIBS PkgConfig::WEBKIT2GTK)
     endif()
 
diff --git a/src/slic3r-shared/CMakeLists.txt b/src/slic3r-shared/CMakeLists.txt
index 9af790d..f32d112 100644
--- a/src/slic3r-shared/CMakeLists.txt
+++ b/src/slic3r-shared/CMakeLists.txt
@@ -1342,7 +1342,6 @@ endif()
 
 find_package(NanoSVG REQUIRED)
 find_package(yoga CONFIG REQUIRED)
-find_package(nlohmann_json 3.11 REQUIRED)
 find_package(EXPAT CONFIG REQUIRED)
 find_package(pugixml CONFIG REQUIRED)
 
@@ -1428,7 +1427,7 @@ target_link_libraries(slic3r-shared PUBLIC
         pugixml::pugixml
         range-v3::range-v3
         libcereal
-        libdeflate::libdeflate_static
+        libdeflate::libdeflate_shared
 )
 target_compile_definitions(slic3r-shared PUBLIC ${SLIC3R_YAML_DEFINE} ${USE_NATIVE_MENU_DEFINE})
 if (SLIC3R_SENTRY_DSN)