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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Problem 1 can be solved by flipping the order. But Problem 2 would remain as it doesn't depend on the order.

Honestly, we should just remove the second test. We just treat these things as libraries and it doesn't make sense for a test to ensure that `-lstdc++` doesn't exist on the user's system or whatever.

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