When AM_SILENT_RULES is available, use it to strip down the output
of make so we can see what's important rather than gigantic long
compile lines.
Use 'make V=1' to see everything again.
Fix a couple of places where we had 'cmp' rather than 'cmp' and were
getting standard-error spew about missing files when generating
enum-types.h files.
http://bugzilla.gnome.org/show_bug.cgi?id=591002