Fixed bug 3975 - Add GLES2 support for macOS via ANGLE library

Andrey

Seems latest google angle library successfully built & tested under macOS'es.

https://github.com/google/angle

We need to use GLES2 to implement true cross-platform code.

include/SDL_config_macosx.h

@@ -179,10 +179,20 @@
 #define SDL_VIDEO_RENDER_OGL    1
 #endif
 
+#ifndef SDL_VIDEO_RENDER_OGL_ES2
+#define SDL_VIDEO_RENDER_OGL_ES2 1
+#endif
+
 /* Enable OpenGL support */
 #ifndef SDL_VIDEO_OPENGL
 #define SDL_VIDEO_OPENGL    1
 #endif
+#ifndef SDL_VIDEO_OPENGL_ES2
+#define SDL_VIDEO_OPENGL_ES2    1
+#endif
+#ifndef SDL_VIDEO_OPENGL_EGL
+#define SDL_VIDEO_OPENGL_EGL    1
+#endif
 #ifndef SDL_VIDEO_OPENGL_CGL
 #define SDL_VIDEO_OPENGL_CGL    1
 #endif