[clang] [openmp] [OpenMP] Respect LLVM per-target install directories (PR #83282)

[Ye Luo via cfe-commits]

ye-luo wrote:

It seems being installed twice both under `lib` and `lib/x86_64-unknown-linux-gnu`. files are the identical as diff show nothing.

https://github.com/llvm/llvm-project/pull/83282