Please replace the BuildRequires: glibc-headers with BuildRequires: gcc. The new Fedora packaging guidelines require you define all the things you need in the buildroot to build [1].

Given that this package has C code it should BuildRequires: gcc, and that is sufficient to bring in all of the required core C libraries and headers to compile C code.

The reason I'm asking is because glibc-headers may or may not be removed in the future and it isn't sufficient to guarantee the package builds.

[1] https://fedoraproject.org/wiki/Packaging:Guidelines#BuildRequires_2