[llvm] [Test] Mark a number of libcall tests `nounwind` (PR #148329)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/23360

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang-Unit :: ./AllClangUnitTests/15/48' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/Users/buildbot/buildbot-root/aarch64-darwin/build/tools/clang/unittests/./AllClangUnitTests-Clang-Unit-61031-15-48.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=48 GTEST_SHARD_INDEX=15 /Users/buildbot/buildbot-root/aarch64-darwin/build/tools/clang/unittests/./AllClangUnitTests
--

Script:
--
/Users/buildbot/buildbot-root/aarch64-darwin/build/tools/clang/unittests/./AllClangUnitTests --gtest_filter=DirectoryWatcherTest.AddFiles
--
/Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/clang/unittests/DirectoryWatcher/DirectoryWatcherTest.cpp:257: Failure
Value of: WaitForExpectedStateResult.wait_for(EventualResultTimeout) == std::future_status::ready
  Actual: false
Expected: true
The expected result state wasn't reached before the time-out.

/Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/clang/unittests/DirectoryWatcher/DirectoryWatcherTest.cpp:260: Failure
Value of: TestConsumer.result().has_value()
  Actual: false
Expected: true


/Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/clang/unittests/DirectoryWatcher/DirectoryWatcherTest.cpp:257
Value of: WaitForExpectedStateResult.wait_for(EventualResultTimeout) == std::future_status::ready
  Actual: false
Expected: true
The expected result state wasn't reached before the time-out.

/Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/clang/unittests/DirectoryWatcher/DirectoryWatcherTest.cpp:260
Value of: TestConsumer.result().has_value()
  Actual: false
Expected: true



********************


```

</details>

https://github.com/llvm/llvm-project/pull/148329