wlserver: Wait for steamcompmgr to shutdown before cleaning up xwayland

Makes shutdown cleaner

src/steamcompmgr.cpp

@@ -213,6 +213,8 @@ extern bool g_bIntegerScale;
 
 bool			synchronize;
 
+std::mutex g_SteamCompMgrXWaylandServerMutex;
+
 enum HeldCommitTypes_t
 {
 	HELD_COMMIT_BASE,
@@ -4286,6 +4288,8 @@ steamcompmgr_main(int argc, char **argv)
 	int vblankFD = vblank_init();
 	assert( vblankFD >= 0 );
 
+	std::unique_lock<std::mutex> xwayland_server_guard(g_SteamCompMgrXWaylandServerMutex);
+
 	// Initialize any xwayland ctxs we have
 	{
 		gamescope_xwayland_server_t *server = NULL;

src/wlserver.cpp

@@ -817,6 +817,8 @@ void wlserver_unlock(void)
 	pthread_mutex_unlock(&waylock);
 }
 
+extern std::mutex g_SteamCompMgrXWaylandServerMutex;
+
 void wlserver_run(void)
 {
 	struct pollfd pollfd = {
@@ -851,6 +853,8 @@ void wlserver_run(void)
 		}
 	}
 
+	// Released when steamcompmgr closes.
+	std::unique_lock<std::mutex> xwayland_server_guard(g_SteamCompMgrXWaylandServerMutex);
 	// We need to shutdown Xwayland before disconnecting all clients, otherwise
 	// wlroots will restart it automatically.
 	wlserver.wlr.xwayland_servers.clear();