UI: Update python linkage for older compilers

Move the python linkage after the obs target is defined so that we can
also add linker flags to preserve the unused python linkage. This is
required before GCC 11.

UI/CMakeLists.txt

@@ -160,15 +160,6 @@ elseif(UNIX)
 		Qt5::Gui
 		Qt5::GuiPrivate)
 
-	# python symbols must be in the global symbol table
-	# so we link the main executable to python if we expect
-	# obs-scripting python support to be enabled.
-	# see: https://github.com/obsproject/obs-studio/issues/2222 and https://bugs.python.org/issue36721
-	if(NOT DISABLE_PYTHON AND PYTHONLIBS_FOUND)
-		set(obs_PLATFORM_LIBRARIES
-			${obs_PLATFORM_LIBRARIES}
-			${PYTHON_LIBRARIES})
-	endif()
 
 	if("${CMAKE_SYSTEM_NAME}" MATCHES "FreeBSD")
 		list(APPEND obs_PLATFORM_LIBRARIES
@@ -489,6 +480,19 @@ if (UNIX AND UNIX_STRUCTURE AND NOT APPLE)
 	add_subdirectory(xdg-data)
 endif()
 
+if (UNIX AND NOT APPLE)
+	# python symbols must be in the global symbol table
+	# so we link the main executable to python if we expect
+	# obs-scripting python support to be enabled.
+	# see: https://github.com/obsproject/obs-studio/issues/2222 and https://bugs.python.org/issue36721
+	if(NOT DISABLE_PYTHON AND PYTHONLIBS_FOUND)
+		target_link_libraries(obs ${PYTHON_LIBRARIES})
+		set_target_properties(obs PROPERTIES LINK_FLAGS "-Wl,--no-as-needed")
+		# Use this after cmake 3.13 aka we drop ubuntu 18.04.
+		# target_link_options(obs PRIVATE "LINKER:-no-as-needed")
+	endif()
+endif()
+
 add_subdirectory(frontend-plugins)
 if(WIN32)
 	add_subdirectory(win-update/updater)