Re-enable signal tests when cross-compiling
Re-enable signal tests when cross-compiling

The glib-genmarshal tool has been rewritten in Python, which means we
can run it when cross-compiling.

https://bugzilla.gnome.org/show_bug.cgi?id=784528

johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib