Fix the Mac embedder build (#6525)

shell/platform/embedder/embedder.cc

@@ -89,6 +89,8 @@ static bool IsRendererValid(const FlutterRendererConfig* config) {
   return false;
 }
 
+#if OS_LINUX || OS_WIN
+
 static void* DefaultGLProcResolver(const char* name) {
   static fml::RefPtr<fml::NativeLibrary> proc_library =
       fml::NativeLibrary::CreateForCurrentProcess();
@@ -96,6 +98,8 @@ static void* DefaultGLProcResolver(const char* name) {
       const_cast<uint8_t*>(proc_library->ResolveSymbol(name)));
 }
 
+#endif  // OS_LINUX || OS_WIN
+
 static shell::Shell::CreateCallback<shell::PlatformView>
 InferOpenGLPlatformViewCreationCallback(
     const FlutterRendererConfig* config,