SDL: cmake: append to COMPILE_FLAGS property

SDL Commits
1 
From 1064fdee8c071faad48c6a26289161fec5da02b5 Mon Sep 17 00:00:00 2001
From: Anonymous Maarten <[EMAIL REDACTED]>
Date: Thu, 6 Oct 2022 05:04:51 +0200
Subject: [PATCH] cmake: append to COMPILE_FLAGS property

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index bc4510a2735c..5867e5ba0d8b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2004,7 +2004,7 @@ elseif(APPLE)
       set(SDL_FRAMEWORK_COREHAPTICS 1)
     else()
       file(GLOB JOYSTICK_SOURCES ${SDL2_SOURCE_DIR}/src/joystick/darwin/*.c)
-      set_source_files_properties(${MFI_JOYSTICK_SOURCES} PROPERTIES COMPILE_FLAGS -fobjc-weak)
+      set_property(SOURCE ${MFI_JOYSTICK_SOURCES} APPEND_STRING PROPERTY COMPILE_FLAGS " -fobjc-weak")
       check_objc_source_compiles("
           #include <AvailabilityMacros.h>
           #include <TargetConditionals.h>