UI: Fix Qt platform override in CMake 3

This override is still needed until Qt minimum version requirement is
increased to at least 6.3.0.

ui-config.h.in and CMake 2 are modified to avoid USE_XDG redefinition in
CMake 3.

UI/cmake/legacy.cmake

@@ -504,16 +504,22 @@ elseif(OS_POSIX)
     target_compile_options(obs PRIVATE -Wno-unqualified-std-cast-call)
   endif()
 
-  if(OS_LINUX AND ENABLE_WHATSNEW)
-    find_package(MbedTLS)
-    find_package(nlohmann_json REQUIRED)
-    if(NOT MBEDTLS_FOUND)
-      obs_status(FATAL_ERROR "mbedTLS not found, but required for WhatsNew support on Linux")
+  if(OS_LINUX)
+    if(USE_XDG)
+      target_compile_definitions(obs PRIVATE USE_XDG)
     endif()
 
-    target_sources(obs PRIVATE update/crypto-helpers.hpp update/crypto-helpers-mbedtls.cpp update/shared-update.cpp
-                               update/shared-update.hpp update/update-helpers.cpp update/update-helpers.hpp)
-    target_link_libraries(obs PRIVATE Mbedtls::Mbedtls nlohmann_json::nlohmann_json OBS::blake2)
+    if(ENABLE_WHATSNEW)
+      find_package(MbedTLS)
+      find_package(nlohmann_json REQUIRED)
+      if(NOT MBEDTLS_FOUND)
+        obs_status(FATAL_ERROR "mbedTLS not found, but required for WhatsNew support on Linux")
+      endif()
+
+      target_sources(obs PRIVATE update/crypto-helpers.hpp update/crypto-helpers-mbedtls.cpp update/shared-update.cpp
+                                 update/shared-update.hpp update/update-helpers.cpp update/update-helpers.hpp)
+      target_link_libraries(obs PRIVATE Mbedtls::Mbedtls nlohmann_json::nlohmann_json OBS::blake2)
+    endif()
   endif()
 endif()
 

UI/cmake/os-linux.cmake

@@ -1,5 +1,5 @@
 target_sources(obs-studio PRIVATE platform-x11.cpp)
-target_compile_definitions(obs-studio PRIVATE OBS_INSTALL_PREFIX="${OBS_INSTALL_PREFIX}")
+target_compile_definitions(obs-studio PRIVATE USE_XDG OBS_INSTALL_PREFIX="${OBS_INSTALL_PREFIX}")
 target_link_libraries(obs-studio PRIVATE Qt::GuiPrivate Qt::DBus)
 
 target_sources(obs-studio PRIVATE system-info-posix.cpp)

UI/obs-app.cpp

@@ -1996,7 +1996,8 @@ static int run_program(fstream &logFile, int argc, char *argv[])
 	if (platform_theme && strcmp(platform_theme, "qt5ct") == 0)
 		unsetenv("QT_QPA_PLATFORMTHEME");
 
-#if defined(ENABLE_WAYLAND) && defined(USE_XDG)
+#if defined(ENABLE_WAYLAND) && defined(USE_XDG) && \
+	QT_VERSION < QT_VERSION_CHECK(6, 3, 0)
 	/* NOTE: Qt doesn't use the Wayland platform on GNOME, so we have to
 	 * force it using the QT_QPA_PLATFORM env var. It's still possible to
 	 * use other QPA platforms using this env var, or the -platform command

UI/ui-config.h.in

@@ -1,7 +1,5 @@
 #pragma once
 
-#cmakedefine USE_XDG
-
 #define OAUTH_BASE_URL "@OAUTH_BASE_URL@"
 
 #define TWITCH_CLIENTID "@TWITCH_CLIENTID@"