OGL: Warn if buffer_storage isn't available.

Yes, this commit is only to blame OSX and Mali. Through the former supports unsynchronized mappings, the latter supports *no* way to stream dynamic data at all. Let's try to make bad news, as they ignore friendly feature requests. Maybe we just need to make more noise...

Source/Core/VideoBackends/OGL/Render.cpp

@@ -730,6 +730,16 @@ Renderer::Renderer()
                                    g_ogl_config.gl_renderer, g_ogl_config.gl_version),
                   5000);
 
+  if (!g_ogl_config.bSupportsGLBufferStorage && !g_ogl_config.bSupportsGLPinnedMemory)
+  {
+    OSD::AddMessage(
+        StringFromFormat("Your OpenGL driver does not support %s_buffer_storage.",
+                         GLInterface->GetMode() == GLInterfaceMode::MODE_OPENGLES3 ? "EXT" : "ARB"),
+        60000);
+    OSD::AddMessage("This device's performance will be terrible.", 60000);
+    OSD::AddMessage("Please ask your device vendor for an updated OpenGL driver.", 60000);
+  }
+
   WARN_LOG(VIDEO, "Missing OGL Extensions: %s%s%s%s%s%s%s%s%s%s%s%s%s%s",
            g_ActiveConfig.backend_info.bSupportsDualSourceBlend ? "" : "DualSourceBlend ",
            g_ActiveConfig.backend_info.bSupportsPrimitiveRestart ? "" : "PrimitiveRestart ",