[clang] [clang] Support --sysroot= for ${arch}-windows-msvc targets (PR #96417)

[via cfe-commits]

trcrsired wrote:

> If I had to pick a best approach to recommend, I like the idea of implementing case-insensitive header search, and wiring that into a `clang` driver `--winsysroot` flag, so it's just unpack and go, but I don't expect everyone will agree, and that's OK, so in short, I think we should merge the PR.

I think in the perfect world, microsoft should themselves just adopt the standard sysroot behavior for windows. I am willing to have a discussion with microsoft developers themselves.

https://github.com/llvm/llvm-project/pull/96417