Provide rules_pkg rpmbuild and git toolchain

[malt3]

Is your feature request related to a problem? Please describe.

rules_pkg depends on a rpmbuild toolchain to be available to package binaries as rpms in the pkg_rpm rule.
There is a method to load rpmbuild from the host path (which is non-hermetic).

EDIT: rules_pkg also has a git toolchain. I think we could provide that as well. The same points apply.

Describe the solution you'd like

nixpkgs contains rpmbuild and could provide a rpmbuild toolchain as required by rules_pkg.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

• Not provide rpmbuild via rules_nixpkgs and have failing builds if developers don't have it on their system
• Package rpmbuild myself

Additional context

I would be happy to implement this (if the maintainers like the idea).

[benradf]

Hi @malt3, thanks for your interest in adding this functionality.

A pull request would be welcome. I'd suggest putting the new toolchains under toolchains/pkg/, and if you have the time to add an example as well, that would be great.