settings: Move settings sanitization to its own function

Creates a new function that can be expanded later to fix other settings that are known to cause emulation errors across executables.

src/core/settings.cpp

@@ -184,4 +184,10 @@ void RestoreGlobalState() {
     values.sound_index.SetGlobal(true);
 }
 
+void Sanitize() {
+    values.use_asynchronous_gpu_emulation.SetValue(
+        values.use_asynchronous_gpu_emulation.GetValue() ||
+        values.use_multi_core.GetValue());
+}
+
 } // namespace Settings