[llvm] [Offload] Make OffloadAPI error messages more readable (PR #140728)

[Ross Brunton via llvm-commits]

RossBrunton wrote:

Example output on my system:

```
FAIL: Offload-Unit :: OffloadAPI/./offload.unittests/33/35 (4 of 35)
******************** TEST 'Offload-Unit :: OffloadAPI/./offload.unittests/33/35' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/ross/build/llvm-project.release/runtimes/runtimes-bins/offload/unittests/OffloadAPI/./offload.unittests-Offload-Unit-780349-33-35.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARD
S=35 GTEST_SHARD_INDEX=33 /home/ross/build/llvm-project.release/runtimes/runtimes-bins/offload/unittests/OffloadAPI/./offload.unittests
--

Script:
--
/home/ross/build/llvm-project.release/runtimes/runtimes-bins/offload/unittests/OffloadAPI/./offload.unittests --gtest_filter=olWaitEventTest.Success/AMDGPU_gfx1100
--
/home/ross/llvm-project/offload/unittests/OffloadAPI/event/olWaitEvent.cpp:26: Failure
Failed
olWaitEvent(Event) returned OL_ERRC_UNIMPLEMENTED: synchronize event not implemented


/home/ross/llvm-project/offload/unittests/OffloadAPI/event/olWaitEvent.cpp:26
Failed
olWaitEvent(Event) returned OL_ERRC_UNIMPLEMENTED: synchronize event not implemented



********************
********************
Failed Tests (1):
  Offload-Unit :: OffloadAPI/./offload.unittests/olWaitEventTest/Success/AMDGPU_gfx1100
```

https://github.com/llvm/llvm-project/pull/140728