[clang] [Clang] Respect `-fno-slp-vectorize` for the LTO pipeline (PR #201585)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-aarch64-out-of-tree` running on `linaro-flang-aarch64-out-of-tree` while building `clang` at step 11 "test-build-flang-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/53/builds/31440

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

```
Step 11 (test-build-flang-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
...
53.305 [2/1/3] Linking CXX executable unittests/Frontend/FlangFrontendTests
95.812 [1/1/4] Linking CXX executable unittests/Semantics/OpenMPUtilsTests
95.812 [0/1/4] Running the Flang regression tests
llvm-lit: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/llvm-project/flang/test/lit.cfg.py:182: warning: Intrinsic modules not in driver default paths: disabling most tests; Use FLANG_TEST_ENABLE_MODULES=ON to force-enable
llvm-lit: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/llvm-project/flang/test/lit.cfg.py:191: warning: OpenMP modules found not in driver default paths: OpenMP tests disabled; Use FLANG_TEST_ENABLE_OPENMP=ON to force-enable
llvm-lit: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/llvm-project/flang/test/lit.cfg.py:196: note: using flang: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/build_flang/bin/flang
llvm-lit: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/llvm-project/flang/test/lit.cfg.py:197: note: using flang implicit search paths: 
llvm-lit: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/llvm-project/flang/test/lit.cfg.py:200: note: using flang extra search paths: 
llvm-lit: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/llvm-project/llvm/utils/lit/lit/llvm/config.py:569: note: using clang: /home/tcwg-buildbot/worker/flang-aarch64-out-of-tree/build_llvm/bin/clang
-- Testing: 4605 tests, 256 workers --
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=1297.866845

```

</details>

https://github.com/llvm/llvm-project/pull/201585