[OpenMP][Offload] Fix flang offload test (#208829)
This PR attempts to address the remaining flang offload test failure
after https://github.com/llvm/llvm-project/pull/208617. Bot:
https://lab.llvm.org/buildbot/#/builders/67/builds/8412
The problem with is test is that `foo__l8` kernel was not linked into
device image without explicitly use the amdgpu-amd-amdhsa triple in the
compilation. It only happened to this specific test.
Local test results after fix:
```
Testing Time: 146.44s
Total Discovered Tests: 3478
Skipped : 77 (2.21%)
Unsupported : 341 (9.80%)
Passed : 3055 (87.84%)
Expectedly Failed: 5 (0.14%)
```
