gmain: Synchronize access to is_running flag of GMainLoop
gmain: Synchronize access to is_running flag of GMainLoop

Synchronize access to is_running field of GMainLoop to ensure that
g_main_loop_is_running is thread safe.

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib