[clang] [clang-sycl-linker] Make AOT temp files land relative to cwd, not -o's dir (PR #224506)

[Ayan Khan via cfe-commits]

ThunderKhan wrote:

One thing that might be worth considering is parallel invocations with the same output basename but different output directories. With the basename-only approach, both could end up using the same intermediate .spv and .out files in the cwd.

Maybe it would be worth keeping some per-invocation uniqueness here while still using the output basename as the stem.

https://github.com/llvm/llvm-project/pull/224506