SDL: Fix build with Xcode < 7 (2df39)

From 2df39e64ab481bebb97378a50c97e37a52da6bc8 Mon Sep 17 00:00:00 2001
From: Joshua Root <[EMAIL REDACTED]>
Date: Sun, 27 Nov 2022 11:27:19 +1100
Subject: [PATCH] Fix build with Xcode < 7

The _Nullable attribute is not available in older versions.

(cherry picked from commit 9a64aa6f95298bf459f8b9dca583df7064956cd9)
---
 src/video/cocoa/SDL_cocoaopengl.m | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/video/cocoa/SDL_cocoaopengl.m b/src/video/cocoa/SDL_cocoaopengl.m
index 2cdbc17e9f0c..58df449a3ac6 100644
--- a/src/video/cocoa/SDL_cocoaopengl.m
+++ b/src/video/cocoa/SDL_cocoaopengl.m
@@ -44,6 +44,16 @@
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
+/* _Nullable is available starting Xcode 7 */
+#ifdef __has_feature
+#if __has_feature(nullability)
+#define HAS_FEATURE_NULLABLE
+#endif
+#endif
+#ifndef HAS_FEATURE_NULLABLE
+#define _Nullable
+#endif
+
 static SDL_bool SDL_opengl_async_dispatch = SDL_FALSE;
 
 static void SDLCALL