Avoid accurately computing disk space on iOS and Android (where it can be slow). Add a setting.

UI/GameSettingsScreen.cpp

@@ -1286,6 +1286,11 @@ void GameSettingsScreen::CreateSystemSettings(UI::ViewGroup *systemSettings) {
 	SavePathInOtherChoice->OnClick.Handle(this, &GameSettingsScreen::OnMemoryStickOther);
 	const bool myDocsExists = W32Util::UserDocumentsPath().size() != 0;
 
+	if (!System_GetPropertyBool(SYSPROP_CAN_GET_FREE_SPACE_FAST)) {
+		// It might be slow, so use an option.
+		systemSettings->Add(new CheckBox(&g_Config.bReportAccurateFreeStorageSpace, sy->T("Report free storage space accurately")));
+	}
+
 	const Path &PPSSPPpath = File::GetExeDirectory();
 	const Path installedFile = PPSSPPpath / "installed.txt";
 	installed_ = File::Exists(installedFile);