[clang] [Clang] Fix padding clearing logic for packed boolean vectors in big endian (PR #224033)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `clang` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/51142

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

```
Step 6 (test-build-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
...
PASS: Flang :: Driver/use-module-error.f90 (5075 of 5086)
PASS: Flang :: Driver/use-module.f90 (5076 of 5086)
PASS: Flang :: Lower/math-lowering/cos.f90 (5077 of 5086)
PASS: Flang :: Lower/math-lowering/cosh.f90 (5078 of 5086)
PASS: Flang :: Semantics/OpenACC/acc-default-none-function.f90 (5079 of 5086)
PASS: Flang :: Semantics/OpenACC/acc-default-none-scalars-strict.f90 (5080 of 5086)
PASS: Flang :: Driver/linker-flags.f90 (5081 of 5086)
PASS: Flang :: Driver/linker-options.f90 (5082 of 5086)
PASS: Flang :: Lower/OpenMP/requires-usm.f90 (5083 of 5086)
PASS: Flang :: Lower/OpenMP/requires.f90 (5084 of 5086)
command timed out: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2282.171845

```

</details>

https://github.com/llvm/llvm-project/pull/224033