[llvm] [Offload][AMDGPU] Make compiler-rt libs visible (PR #209849)

[Kewen Meng via llvm-commits]

Kewen12 wrote:

>The handling of those libraries is supposed to come from the compiler, so if we just pass the files normally they should be included. I don't know why they wouldn't be in this case, unless there's a dependency issue where these tests are running without completing the runtimes builds.

For this case, the error is 
```
ld.lld: error: unable to find library -lclang_rt.builtins
```
seems clang finds the compiler-rt and passes only the lib name to the device linker.

>-L should never be necessary for the resource directory

Yes, I agree. lit should not require to add -L manually. But the driver is not passing the full resource-dir path to the linker. This PR is a workaround to unblock our buildbot: https://lab.llvm.org/buildbot/#/builders/67. The long-term fix should be on the clang side. Pass the full path to the linker. 

https://github.com/llvm/llvm-project/pull/209849