SDL_cocoamodes.m: fix build against older SDKs. Fixes https://github.com/libsdl-org/SDL/issues/5208
diff --git a/src/video/cocoa/SDL_cocoamodes.m b/src/video/cocoa/SDL_cocoamodes.m
index e8ce12d..7d19030 100644
--- a/src/video/cocoa/SDL_cocoamodes.m
+++ b/src/video/cocoa/SDL_cocoamodes.m
@@ -40,6 +40,9 @@
#ifndef MAC_OS_X_VERSION_10_13
#define NSAppKitVersionNumber10_12 1504
#endif
+#if (IOGRAPHICSTYPES_REV < 40)
+#define kDisplayModeNativeFlag 0x02000000
+#endif
static void