build: Add --with(out)-cairo configure option
build: Add --with(out)-cairo configure option

Some builders (e.g. GNOME and jhbuild) hard depend on pangocairo,
and we really don't want to emit a build of pango without support
for it.  So jhbuild can specify --with-cairo, and we'll get
a hard error.

Distrotech/pango,kari-lentz/alpha-pango,danny-ku/pango,kari-lentz/alpha-pango,danny-ku/pango,Distrotech/pango,kari-lentz/alpha-pango,danny-ku/pango,Distrotech/pango,kari-lentz/alpha-pango