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