frontend: Cleanup Qt GuiPrivate linkage

Remove unneeded linkages and guard needed ones for Qt versions earlier
than 6.9.0.

frontend/cmake/os-freebsd.cmake

@@ -7,7 +7,11 @@ target_sources(
     utility/system-info-posix.cpp
 )
 target_compile_definitions(obs-studio PRIVATE OBS_INSTALL_PREFIX="${OBS_INSTALL_PREFIX}")
-target_link_libraries(obs-studio PRIVATE Qt::GuiPrivate Qt::DBus procstat)
+target_link_libraries(obs-studio PRIVATE Qt::DBus procstat)
+
+if(Qt6_VERSION AND Qt6_VERSION VERSION_LESS "6.9.0")
+  target_link_libraries(obs-studio PRIVATE Qt::GuiPrivate)
+endif()
 
 find_package(Libpci REQUIRED)
 target_link_libraries(obs-studio PRIVATE Libpci::pci)

frontend/cmake/os-linux.cmake

@@ -10,7 +10,11 @@ target_compile_definitions(
   obs-studio
   PRIVATE OBS_INSTALL_PREFIX="${OBS_INSTALL_PREFIX}" $<$<BOOL:${ENABLE_PORTABLE_CONFIG}>:ENABLE_PORTABLE_CONFIG>
 )
-target_link_libraries(obs-studio PRIVATE Qt::GuiPrivate Qt::DBus)
+target_link_libraries(obs-studio PRIVATE Qt::DBus)
+
+if(Qt6_VERSION AND Qt6_VERSION VERSION_LESS "6.9.0")
+  target_link_libraries(obs-studio PRIVATE Qt::GuiPrivate)
+endif()
 
 find_package(Libpci REQUIRED)
 target_link_libraries(obs-studio PRIVATE Libpci::pci)

frontend/plugins/aja-output-ui/CMakeLists.txt

@@ -10,8 +10,6 @@ find_package(LibAJANTV2 REQUIRED)
 find_package(Qt6 REQUIRED Widgets)
 
 if(OS_LINUX OR OS_FREEBSD OR OS_OPENBSD)
-  find_package(Qt6 REQUIRED Gui)
-
   find_package(X11 REQUIRED)
 endif()
 
@@ -47,7 +45,6 @@ target_link_libraries(
     Qt::Widgets
     AJA::LibAJANTV2
     $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD>:X11::X11>
-    $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD>:Qt::GuiPrivate>
 )
 
 target_link_options(aja-output-ui PRIVATE $<$<PLATFORM_ID:Windows>:/IGNORE:4099>)

frontend/plugins/decklink-output-ui/CMakeLists.txt

@@ -8,8 +8,6 @@ endif()
 find_package(Qt6 REQUIRED Widgets)
 
 if(OS_LINUX OR OS_FREEBSD OR OS_OPENBSD)
-  find_package(Qt6 REQUIRED Gui)
-
   find_package(X11 REQUIRED)
 endif()
 
@@ -38,7 +36,6 @@ target_link_libraries(
     Qt::Widgets
     "$<$<PLATFORM_ID:Darwin>:$<LINK_LIBRARY:FRAMEWORK,Cocoa.framework>>"
     $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD>:X11::X11>
-    $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD>:Qt::GuiPrivate>
 )
 
 if(OS_WINDOWS)

frontend/plugins/frontend-tools/CMakeLists.txt

@@ -3,7 +3,6 @@ cmake_minimum_required(VERSION 3.28...3.30)
 find_package(Qt6 REQUIRED Widgets)
 
 if(OS_LINUX OR OS_FREEBSD OR OS_OPENBSD)
-  find_package(Qt6 REQUIRED Gui)
   find_package(X11 REQUIRED)
 endif()
 
@@ -65,7 +64,6 @@ target_link_libraries(
     Qt::Widgets
     "$<$<PLATFORM_ID:Darwin>:$<LINK_LIBRARY:FRAMEWORK,Cocoa>>"
     $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD>:X11::X11>
-    $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD>:Qt::GuiPrivate>
 )
 
 add_subdirectory("${CMAKE_SOURCE_DIR}/shared/obs-scripting" "${CMAKE_BINARY_DIR}/shared/obs-scripting")