On oss-fuzz, we build twice, to put together a build that is portable to
the runner containers. On gitlab ci, this is wasteful and contributes to
timeouts on the build-oss-fuzz job. Avoid building twice on gitlab, at
the remote cost of potentially missing some cases that break oss-fuzz
builds.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-Id: <20210809111621.54454-1-alxndr@bu.edu>
Signed-off-by: Thomas Huth <thuth@redhat.com>