I am not exactly sure what are you reporting. Is the problem the unwanted message "posix_spawn avoided (fd close requested)" as specified in the github issue or does createrepo_c not terminate correctly for you and it hangs at the end as per the title? 

If it is the latter could you please provide some more information such as verbose output of the createrepo_c run and if possible a way to reproduce it? For example on what packages does it happen?

It's the latter. Not all of the packages I'm running it on are publicly distributable, but the run on them produces the attached. I had to CtrlC just prior to the Directory Walk Started line. There are 3 repos here, run from a bash script with -vvv.

Created attachment 1575712 [details]
output

I created a PR that should fix this: https://github.com/rpm-software-management/createrepo_c/pull/164

Works wonderfully in my local test package. Let me know when this hits updates-testing and I'll provide Karma. Thank you!

FEDORA-2019-236e6fa2ca has been submitted as an update to Fedora 30. https://bodhi.fedoraproject.org/updates/FEDORA-2019-236e6fa2ca

createrepo_c-0.14.2-1.fc30 has been pushed to the Fedora 30 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2019-236e6fa2ca

createrepo_c-0.14.2-1.fc30 has been pushed to the Fedora 30 stable repository. If problems still persist, please make note of it in this bug report.