[clang] [clang-scan-deps] Infer the tool locations from PATH (PR #108539)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> Ok, thanks for the explanation. This LGTM, but the checks are failing on Windows due to `.exe` extension that's not accounted for. I don't think any of the tests you touched really care about the executable path, so I'd be fine with just removing those check lines.

Ah, thanks. Yeah it's probably best that we remove those checks that don't carry much relevance there. (The main test that really exercise this functionality, that I'm adding here, has a `UNSUPPORTED: system-windows` marking due to using symlinks for setting up the `PATH` test environment though. But that's only an issue with the test - the implementation seems to work fine regardless, as noted when the other tests fail.)

https://github.com/llvm/llvm-project/pull/108539