gitlab: fall back to commit hash in qemu-setup filename

gitlab: fall back to commit hash in qemu-setup filename

Personal repos may not have release tags (v6.0.0, v6.1.0, etc) and this
causes cross_system_build_job to fail when pretty-printing a unique
qemu-setup-*.exe name:

  version="$(git describe --match v[0-9]*)";
             ^^^^^^^^^^ fails ^^^^^^^^^^^
  mv -v qemu-setup*.exe qemu-setup-${version}.exe;

Fall back to the short commit hash if necessary. This fixes CI failures
that Greg Kurz and I experienced in our personal repos.

Cc: Greg Kurz <groug@kaod.org>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220125173454.10381-1-stefanha@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220204204335.1689602-14-alex.bennee@linaro.org>