[llvm] [openmp] [OpenMP][Runtime] Handling crash with `OMP_TARGET_OFFLOAD=DISABLED` and invoking `omp_get_default_device()` (PR #171789)

[via llvm-commits]

https://github.com/jprotze commented:

The runtime tests don't REQUIRE ompt. 

The tests contain a lot of assumptions about the return value of `omp_get_initial_device()` that are not always true. For testing purposes, `omp_get_initial_device()` should probably randomly return `omp_initial_device` or `omp_get_num_devices()`.

I put comments to the most obvious issues.

https://github.com/llvm/llvm-project/pull/171789