[clang] [clang][test] Add more tests for __builtin_clear_padding (PR #205813)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `clang` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/33166

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

```
Step 5 (ninja check 1) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
[155/159] Linking CXX executable unittests/ExecutionEngine/MCJIT/MCJITTests
[156/159] Linking CXX executable unittests/tools/llvm-exegesis/LLVMExegesisTests
[157/159] Linking CXX executable unittests/ObjectYAML/ObjectYAMLTests
[158/159] Linking CXX executable unittests/Passes/Plugins/PluginsTests
[158/159] Running all regression tests
llvm-lit: /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/utils/lit/lit/llvm/config.py:569: note: using split-file: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/split-file
llvm-lit: /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/utils/lit/lit/llvm/config.py:569: note: using yaml2obj: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/yaml2obj
llvm-lit: /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/utils/lit/lit/llvm/config.py:569: note: using llvm-objcopy: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/llvm-objcopy
llvm-lit: /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/utils/lit/lit/llvm/config.py:569: note: using clang: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang
-- Testing: 96047 of 96050 tests, 256 workers --
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1726.906126

```

</details>

https://github.com/llvm/llvm-project/pull/205813