gquark: simplify g_intern_string/g_intern_static_string
gquark: simplify g_intern_string/g_intern_static_string

Move the common code to a quark_intern_string_locked function. This has
no effect on the generated code but makes codebase a bit cleaner.

https://bugzilla.gnome.org/show_bug.cgi?id=768507

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