I had a hard times with debugging scl-utils-build package, where
%__scl_provides and %_scl_requires commands did not eat the whole stdin
%(provided by rpm as pipe), proposed fix in [1].

This caused an immediate exit of the rpmbuild with exit status 141, with
completely zero info about the failure (reproduced on Fedora 25, performing
a mock build against fedora-rawhide-x86_64 chroot).

It would be nice if rpm logged what provides/requires generators
were run, what were the command arguments and what was the exit status.

[1] https://github.com/sclorg/scl-utils/pull/13.