GLib header files annotate every API with a version number.

It is possible to define some constants before including
glib.h which will result in useful compile time warnings.

Setting GLIB_VERSION_MIN_REQUIRED will result in a warning
if libvirt uses an API that was deprecated in the declared
version, or before. Such API usage should be rewritten to
use the documented new replacement API.

Setting GLIB_VERSION_MAX_ALLOWED will result in a warning
if libvirt uses an API that was not introduced until a
version of GLib that's newer than our minimum declared
version. This avoids accidentally using functionality
that is not available on some supported platforms.
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>
Reviewed-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>