Add a method to check whether to run in background instead of checking for macOS

Telegram/SourceFiles/platform/linux/specific_linux.h

@@ -24,6 +24,10 @@ inline void WriteCrashDumpDetails() {
 inline void AutostartRequestStateFromSystem(Fn<void(bool)> callback) {
 }
 
+inline bool RunInBackground() {
+	return false;
+}
+
 inline bool PreventsQuit(Core::QuitReason reason) {
 	return false;
 }