Rework constructHipPath so HIP_PATH env var is lower priority.

[ScottTodd]

Progress on https://github.com/ROCm/TheRock/issues/1200. Tested downstream (via a patch) in https://github.com/ROCm/TheRock/pull/1201.

The HIP SDK sets the HIP_PATH environment variable, which hipcc and hipconfig were using instead of neighboring files.

A robust way to handle this would be to stamp all information about related tools into the tools themselves during packaging, rather than use global state like environment variables or heuristics like scanning the file system. I think once we've progressed further towards rolling out the new ROCm "superrepos" and open source CI/CD we can make those deeper changes. For now, I've extended the brittle logic with another special case.