Two issues:

Please replace the BuildRequires: glibc-headers with BuildRequires: gcc-c++. 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-c++, and that is sufficient to bring in all of the required core C/C++ libraries and headers to compile C/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

Secondly, the Requires: glibc-headers should be removed, it is insufficient to allow Makefile's produced by shedskin to run, and if that is desired it should be replaced by Requires: gcc-g++ (to provide the compiler and headres and libraries to build the resulting translated C++).