main: print the type of signal that stopped us

Unfortunately glib's signal handling doesn't pass the signal type to the
handler but it's easy enough to wrap.

Related to #48
6 jobs for wip/named-signals in 1 minute and 21 seconds (queued for 6 seconds)
Status Name Job ID Coverage
  Container
passed container_fedora #13925082

00:00:11

passed container_ubuntu #13925083

00:00:14

 
  Build
passed build_on_fedora_no_docs #13925085

00:00:56

passed build_on_fedora_with_docs #13925084

00:01:06

passed build_on_ubuntu_no_gir #13925087

00:00:45

passed build_on_ubuntu_with_gir #13925086

00:00:47