build: Update autogen.sh from GNOME template
build: Update autogen.sh from GNOME template

This fixes problems when building with srcdir ≠ builddir.

https://bugzilla.gnome.org/show_bug.cgi?id=763945

GNOME/gupnp,GNOME/gupnp,GNOME/gupnp,GNOME/gupnp