Append mingw_stdthreads to EXTRA_LIBRARIES

Currently for this CMake version, it seems that there is no support to
link other targets to object libraries. I'll add it to EXTRA_LIBRARIES
instead.

src/CMakeLists.txt

@@ -170,6 +170,10 @@ if(LMMS_HAVE_MP3LAME)
 	list(APPEND EXTRA_LIBRARIES mp3lame::mp3lame)
 endif()
 
+IF(LMMS_USE_MINGW_STD_THREADS)
+	list(APPEND EXTRA_LIBRARIES mingw_stdthreads)
+ENDIF()
+
 SET(LMMS_REQUIRED_LIBS ${LMMS_REQUIRED_LIBS}
 	${CMAKE_THREAD_LIBS_INIT}
 	${QT_LIBRARIES}
@@ -207,10 +211,6 @@ FOREACH(LIB ${LMMS_REQUIRED_LIBS})
 	ENDIF()
 ENDFOREACH()
 
-IF(USE_MINGW_STD_THREADS)
-	TARGET_LINK_LIBRARIES(lmmsobjs PRIVATE mingw_stdthreads)
-ENDIF()
-
 IF(LMMS_BUILD_WIN32)
 	SET_TARGET_PROPERTIES(lmms PROPERTIES
 		ENABLE_EXPORTS ON