The cfitsio devel package should not Requires on glibc-headers.

The cfitsio development libraries and headers will be used by developers via BuildRequires, but along with BuildRequires: gcc or BuildRequires: gcc-gfortran to be able to compile.

The compiler will ensure the standard libraries and headers are installed to make sure the cfitsion headers are complete e.g. that #include <stdio.h> works.

There is no need to Require: glibc-headers. The reason I'm asking for the removal of glibc-headers is that the package may or may not go away in the future depending on sub-package restructuring.