bazelbuild
internal(config_settings): make config_setting creation reusable
The PR #1743 explored the idea of creating extra config settings for
each target platform that our toolchain is targetting, however that has
a drawback of not being usable in bzlmod if someone built Python for
a platform that we don't provide a toolchain for and tried to use the
pip.parse machinery with that by providing the
python_interpreter_target. That is a niche usecase, but rules_python
is a core ruleset that should only provide abstractions/helpers that
work in all cases or make it possible to extend things.
This explores a way to decouple the definition of the available
config_settings values and how they are constructed by adding an extra
is_python_config_setting macro, that could be used to declare the
config settings from within the pip.parse hub repo. This makes the
work in #1744 to support whl-only hub repos more self-contained.
Supersedes #1743.
