[OpenMP][Offload][AMDGPU] Fix offload tests failure after the new triple (#208617)

Offload tests failed after introducing the new triple. This PR attempts
to address that. It includes the changes in
https://github.com/llvm/llvm-project/pull/208551. In addition, it also
made following changes:

- Updated flang builder that our buildbot uses;
- Updated the CMakeLists for offload and AMDGPU device runtime (a little
duplications to avoid breaking other buildbots);
- Added per target linker path and mapping for lit substitution/features
in lit config;
- Updated hard-coded check lines in the tests.

This PR reduces the failed offload tests from 246 to 2 on my test runs
locally. Test results and the two failed tests:
```
Failed Tests (2):
   libomptarget :: amdgpu-amd-amdhsa :: offloading/fortran/declare-target-common-block-main.f90
   libomptarget :: amdgpu-amd-amdhsa :: sanitizer/use_after_free_2.c

 Total Discovered Tests: 3478
   Skipped          :   77 (2.21%)
   Unsupported      :  341 (9.80%)
   Passed           : 3053 (87.78%)
   Expectedly Failed:    5 (0.14%)
   Failed           :    2 (0.06%)
```

I was not able to identify the commits for the two failed tests yet
(didn't look like flakiness), will try again later.

Co-authored-by: Jan Patrick Lehr <JanPatrick.Lehr@amd.com>
GitOrigin-RevId: 71fe35814f4b4b5dc88b9caa65f44da5da946df8