gitlab: force dwarf4 format for debuginfo in Fedora rawhide

gitlab: force dwarf4 format for debuginfo in Fedora rawhide

Fedora 34 rawhide has pulled in a new GCC 11 build which now
defaults to dwarf5 format. This format is not compatible with
the pdwtags program used in our test suite to validate the
RPC files.

We have no need for debuginfo in CI except for pdwtags,
so the simplest short term fix is to force the older dwarf
version in the hope that a fixed dwarves release will
arrive before Fedora 34 is released, or GCC 11 becomes more
widespread. Eventually we might need to figure out a way to
probe for compatibility but for now, we'll hope that any
distro with GCC 11 will be able to have a fixed dwarves too.

https://bugzilla.redhat.com/show_bug.cgi?id=1919965
Reviewed-by: Erik Skultety <eskultet@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>