Fixed check for Mac OS X 10.11+ SDK (thanks Edward Rudd!)

include/SDL_config_macosx.h

@@ -176,7 +176,7 @@
 
 /* Enable Vulkan support */
 /* Metal/MoltenVK/Vulkan only supported on 64-bit architectures with 10.11+ */
-#if TARGET_CPU_X86_64
+#if TARGET_CPU_X86_64 && (MAC_OS_X_VERSION_MAX_ALLOWED >= 101100)
 #define SDL_VIDEO_VULKAN 1
 #else
 #define  SDL_VIDEO_VULKAN 0