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

[Ye Luo via cfe-commits]

ye-luo wrote:

```
yeluo at epyc-server:/soft/llvm/main-20240301/lib$ ls libomp* -l
lrwxrwxrwx 1 yeluo yeluo       34 Mar  1 11:18 libomptarget.rtl.amdgpu.so -> libomptarget.rtl.amdgpu.so.19.0git
-r--r--r-- 1 yeluo yeluo 67532024 Mar  1 11:04 libomptarget.rtl.amdgpu.so.19.0git
lrwxrwxrwx 1 yeluo yeluo       32 Mar  1 11:18 libomptarget.rtl.cuda.so -> libomptarget.rtl.cuda.so.19.0git
-r--r--r-- 1 yeluo yeluo 67440504 Mar  1 11:04 libomptarget.rtl.cuda.so.19.0git
lrwxrwxrwx 1 yeluo yeluo       34 Mar  1 11:18 libomptarget.rtl.x86_64.so -> libomptarget.rtl.x86_64.so.19.0git
-r--r--r-- 1 yeluo yeluo 67349472 Mar  1 11:04 libomptarget.rtl.x86_64.so.19.0git
lrwxrwxrwx 1 yeluo yeluo       23 Mar  1 11:18 libomptarget.so -> libomptarget.so.19.0git
-r--r--r-- 1 yeluo yeluo  2686592 Mar  1 11:04 libomptarget.so.19.0git
```
Should libomptarget follow the relocation of libomp.

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