[llvm] [ci] New script to generate test reports as Buildkite Annotations (PR #113447)

[Daniel Thornburgh via llvm-commits]

mysterymath wrote:

Since this relanded, I've been getting pre-commit breakages on a libc change:
https://buildkite.com/llvm-project/github-pull-requests/builds/120029#01933169-a0ae-443c-9de3-0827c512a223

I can't find anything in the logs that indicates that a build or test failure occurred. Does anything jump out to you as to why this might be happening?

It also looks like a coworker's libc change went through without issue:
https://buildkite.com/llvm-project/github-pull-requests/builds/119274#_

```
+ runtimes=
--
  | + runtime_targets=
  | + [[ '' != '' ]]
  | + at-exit
  | + mkdir -p artifacts
  | + ccache --print-stats
  | + shopt -s nullglob
  | + python3 /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-5wwkv-1/llvm-project/github-pull-requests/.ci/generate_test_report.py ':linux: Linux x64 Test Results' linux-x64-test-results
  | Traceback (most recent call last):
  | File "/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-5wwkv-1/llvm-project/github-pull-requests/.ci/generate_test_report.py", line 406, in <module>
  | p = subprocess.Popen(
  | File "/usr/lib/python3.10/subprocess.py", line 971, in __init__
  | self._execute_child(args, executable, preexec_fn, close_fds,
  | File "/usr/lib/python3.10/subprocess.py", line 1796, in _execute_child
  | self.pid = _posixsubprocess.fork_exec(
  | TypeError: expected str, bytes or os.PathLike object, not NoneType
  | 🚨 Error: The command exited with status 1
  | user command error: exit status 1
```



https://github.com/llvm/llvm-project/pull/113447