Disable FAM support in RHEL
    
    FAM support in GLib requires Gamin component, which has various issues
    and is unmaintained for years. GLib is the only component that requires
    it in RHEL. So let's do not build the optional glib2-fam subpackage on
    RHEL so Gamin can be dropped out from there. I am not doing the same
    change for Fedora as there are more components that require Gamin. So
    the subpackage can be held there yet for some time. The only reason why
    this change hasn't been done earlier is the fact that FAM support was
    needed for DConf functionality when the home directory is on NFS. But
    this shouldn't be a problem nowadays thanks to the following commit:
    https://gitlab.gnome.org/GNOME/glib/-/commit/7427bb71.