[clang] [clang-sycl-linker] AOT-compile split modules concurrently (PR #224548)

[Alexey Bader via cfe-commits]

https://github.com/bader approved this pull request.

LGTM, but I'd like @sarnex to review before the merge if possible.

https://github.com/llvm/llvm-project/pull/224548