If things build fine with `stdenvNoCC`, let them use that. If tools
might be prefixed, prepare for that, either by directly splicing or just
using the env vars provided by the wrapper setup-hooks.
Co-authored-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>
Not every package that needs xcbuild will want to use its build phase.
I have moved the xcbuild setup hook to the new attribute xcbuildHook.
This means that dontUseXcbuild is no longer needed. If you just need
to call xcbuild on its own you can just refer to xcbuild.
This includes adding a new xcbuild-based libutil build to test the waters a bit there.
We'll need to get xcbuild into the stdenv bootstrap before we can make the main build,
but it's nice to see that it can work.
