scanner: Support boolean constants

Aliasing TRUE or FALSE is not very common, but done occasionally
for extra clarity. Namely G_SOURCE_REMOVE / G_SOURCE_CONTINUE are
self-explanatory, unlike the "raw" booleans.

https://bugzilla.gnome.org/show_bug.cgi?id=719566
Post-release version bump to match glib
Update glib annotations from git master
scanner: make sure we pass CFLAGS to cpp

When doing the source scanning in giscanner, make sure we pass the
user's CFLAGS environment variable to the compiler, as we do for the
dumper.

https://bugzilla.gnome.org/show_bug.cgi?id=720063
dumper: use 'cc' as the default C compiler

If $(CC) is unset, use 'cc' instead of 'gcc' as the default compiler.

This matches the behaviour used in the source scanner.

https://bugzilla.gnome.org/show_bug.cgi?id=720066