MacOS: Silence OpenGL deprecation warnings.

OpenGL is deprecated by Apple and triggers a warning when used. The goal
is that OpenGL is replaced by Metal backend, but we are not there yet.

To improve tracability of new warnings we hide deprecation warnings
when the GHOST_ContextCGL.h file is included.

NOTE: This change silences other deprecation warnings as well.

intern/ghost/intern/GHOST_SystemCocoa.mm

@@ -16,6 +16,12 @@
 #include "GHOST_WindowCocoa.h"
 #include "GHOST_WindowManager.h"
 
+/* Don't generate OpenGL deprecation warning. This is a known thing, and is not something easily
+ * solvable in a short term. */
+#ifdef __clang__
+#  pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#endif
+
 #include "GHOST_ContextCGL.h"
 
 #ifdef WITH_VULKAN_BACKEND

intern/ghost/intern/GHOST_WindowCocoa.mm

@@ -6,6 +6,12 @@
 #include "GHOST_Debug.h"
 #include "GHOST_SystemCocoa.h"
 
+/* Don't generate OpenGL deprecation warning. This is a known thing, and is not something easily
+ * solvable in a short term. */
+#ifdef __clang__
+#  pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#endif
+
 #include "GHOST_ContextCGL.h"
 
 #ifdef WITH_VULKAN_BACKEND

source/blender/gpu/metal/mtl_context.hh

@@ -12,6 +12,12 @@
 #include "GPU_common_types.h"
 #include "GPU_context.h"
 
+/* Don't generate OpenGL deprecation warning. This is a known thing, and is not something easily
+ * solvable in a short term. */
+#ifdef __clang__
+#  pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#endif
+
 #include "intern/GHOST_Context.h"
 #include "intern/GHOST_ContextCGL.h"
 #include "intern/GHOST_Window.h"