MacOS: disable mode selection button if backend is not supported

Author: azhirnov

NativeApp/Apple/Source/Classes/OSX/ModeSelectionViewController.mm

@@ -37,6 +37,21 @@ - (void) setWindowTitle:(NSString*) title
     [mainWindow setTitle:title];
 }
 
+- (void)viewDidLoad
+{
+#if !GL_SUPPORTED && !GLES_SUPPORTED
+    ((NSButton*)self.view.subviews[0]).enabled = false;
+#endif
+
+#if !VULKAN_SUPPORTED
+    ((NSButton*)self.view.subviews[1]).enabled = false;
+#endif
+
+#if !METAL_SUPPORTED
+    ((NSButton*)self.view.subviews[2]).enabled = false;
+#endif
+}
+
 - (void) terminateApp:(NSString*) error
 {
     NSAlert *alert = [[NSAlert alloc] init];