Enable glib_debug
This was previously done with Fedora 40
See https://gitlab.gnome.org/GNOME/glib/-/issues/3380
That issue erroneously says that Debian had already enabled this feature because Debian is enabling meson auto features by default. In reality, that requires dh compat level 14 which is only used by a few packages.
Most Debian GNOME packages do enable auto features if the package uses auto features, but this was only done for glib now (as in earlier today in Salsa).
See docs/macros.md for documentation about what glib_debug does. When this build option is enabled, '-DG_ENABLE_DEBUG'
is added to the build.
@smcv Could I have your opinion on this build change?