Just as a side-note, it's a faulty query. You need to query src.rpm
repositories if you want to examine BuildRequires.
If you don't want to do that, examine dependencies on libqxt to get
a first overview. Those likely are the result of a build dependency:
# repoquery --whatrequires libqxt
Here's a repoquery for BuildRequires:
# repoquery --archlist=src --whatrequires libqxt-devel --enablerepo=fedora-source