%pyproject_buildrequires: Generate BuildRequires for this package
    
    This package is already installed -- otherwise the macro would not even exist.
    
    However, since python3-devel has started to Require pyproject-rpm-macros,
    it is no longer possible to use `repoquery --whatrequires pyproject-rpm-macros`
    to get a reliable list of packages that use the macros.
    
    This was, all packages that use %pyproject_buildrequires will BuildRequire the macros explicitly.
    
    (In the future, we could even include a stub version of %pyproject_buildrequires
    in pyproject-srpm-macros (always installed in the buildroot),
    that only echoes this package,
    so packagers would not need to manually BuildRequire anything at all.)