Settings: Don't enable fastmem without recompiler

Don't need to bother allocating memory otherwise.

src/core/settings.cpp

@@ -1012,6 +1012,10 @@ void Settings::FixIncompatibleSettings(bool display_osd_messages)
   }
 #endif
 
+  // fastmem should be off if we're not using the intepreter, save the allocation
+  if (g_settings.cpu_execution_mode != CPUExecutionMode::Recompiler)
+    g_settings.cpu_fastmem_mode = CPUFastmemMode::Disabled;
+
   if (g_settings.IsRunaheadEnabled() && g_settings.rewind_enable)
   {
     if (display_osd_messages)