[windows] Patch hipcc to use HIP_PATH env var at lower priority.

[ScottTodd]

Fixes #1200. Sent upstream for review as well at ROCm/llvm-project#289.

The HIP SDK sets the HIP_PATH environment variable, which hipcc and hipconfig were using instead of neighboring files. This resulted in errors like this when the HIP SDK was installed:

λ .\build\compiler\hipcc\dist\bin\hipcc --version
'C:\Program' is not recognized as an internal or external command,
operable program or batch file.
The system cannot find the path specified.
'nvcc' is not recognized as an internal or external command,
operable program or batch file.
Device not supported - Defaulting to AMD
HIP version: 6.2.41512-db3292736
The system cannot find the path specified.
failed to execute:""C:\Program Files\AMD\ROCm\6.2\lib\llvm\bin\clang.exe"  --driver-mode=g++ -O3 -fuse-ld=lld --ld-path="C:\Program Files\AMD\ROCm\6.2\lib\llvm\bin\lld-link.exe" -Llib --hip-link  --version"

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.