[clang] [clang][modules] Determine if the SDK supports builtin modules independent of the target (PR #134005)

[Ian Anderson via cfe-commits]

ian-twilightcoder wrote:

> LGTM. I was a bit worried about the fallout that other target triples using the same sdks would now opt into this behavior but if that were the case they'd already be running into modularization errors (e.g. `found_incompatible_headers__check_search_paths`)

Other target triples using the same sdks will now opt into this behavior, but there's no way they could've built with modules before.

https://github.com/llvm/llvm-project/pull/134005