CMake: Use -fapplication-extension when building Qt libraries on macOS

Needed to avoid linker warnings transformed into errors, when linking
QtWebEngine with qmake mixing.

ld: warning: linking against a dylib which is not safe for use in
application extensions:

The flag is added to libraries and plugins, unless opted out.

CMake equivalent of 944110089d

Task-number: QTBUG-83929
Task-number: QTBUG-75666
Change-Id: I3e9acca4712c9a266bf54c6e35e2fd2c0096692b
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

cmake/QtInternalTargets.cmake

@@ -204,3 +204,22 @@ function(qt_auto_detect_fpmath)
     endif()
 endfunction()
 qt_auto_detect_fpmath()
+
+function(qt_handle_apple_app_extension_api_only)
+    if(APPLE)
+        # Build Qt libraries with -fapplication-extension. Needed to avoid linker warnings
+        # transformed into errors on darwin platforms.
+        set(flags "-fapplication-extension")
+        set(genex_condition "$<NOT:$<BOOL:$<TARGET_PROPERTY:QT_NO_APP_EXTENSION_ONLY_API>>>")
+        set(flags "$<${genex_condition}:${flags}>")
+        target_compile_options(PlatformModuleInternal INTERFACE ${flags})
+        target_link_options(PlatformModuleInternal INTERFACE ${flags})
+        target_compile_options(PlatformPluginInternal INTERFACE ${flags})
+        target_link_options(PlatformPluginInternal INTERFACE ${flags})
+    endif()
+endfunction()
+function(qt_disable_apple_app_extension_api_only target)
+    set_target_properties("${target}" PROPERTIES QT_NO_APP_EXTENSION_ONLY_API TRUE)
+endfunction()
+
+qt_handle_apple_app_extension_api_only()

src/plugins/platforms/cocoa/CMakeLists.txt

@@ -63,6 +63,10 @@ qt_internal_add_plugin(QCocoaIntegrationPlugin
         Qt::ThemeSupportPrivate
 )
 
+# special case begin
+qt_disable_apple_app_extension_api_only(QCocoaIntegrationPlugin)
+# special case end
+
 # Resources:
 set(qcocoaresources_resource_files
     "images/sizeallcursor.png"

src/plugins/platforms/ios/CMakeLists.txt

@@ -37,6 +37,10 @@ add_qt_plugin(QIOSIntegrationPlugin
         Qt::GuiPrivate
 )
 
+# special case begin
+qt_disable_apple_app_extension_api_only(QIOSIntegrationPlugin)
+# special case end
+
 #### Keys ignored in scope 1:.:.:kernel.pro:<TRUE>:
 # OTHER_FILES = "quiview_textinput.mm" "quiview_accessibility.mm"
 

src/plugins/platforms/xcb/CMakeLists.txt

@@ -64,6 +64,10 @@ qt_add_module(XcbQpa
         XKB::XKB
 )
 
+# special case begin
+qt_disable_apple_app_extension_api_only(XcbQpa)
+# special case end
+
 ## Scopes:
 #####################################################################