This reworks some of xcbuild logic to make it more compatible with
Apple’s SDK.
- Add a fake version of xcrun & xcode-select
- Cleanup platform generation. Clang does not like having 20 char
hashes in sysroot so it is much easier to just build the parent
directory for each runCommand. This is a little awkward but I have
renamed everything with an added ‘s’ to make the distinction more clear.
- Cleaned up wrapper.nix in some different ways
- Reuse some versioning logic so that we don’t end up with two
different versions of Xcode or SDK reported.
