[clang] [OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering (PR #123867)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/17521

<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 :: OpenMP/simd_conservative_ordered.c' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 3: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/clang -g0 -fopenmp-simd -x c -S -emit-llvm /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c -o - | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck --allow-unused-prefixes /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/clang -g0 -fopenmp-simd -x c -S -emit-llvm /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c -o -
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck --allow-unused-prefixes /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c:5:10: fatal error: 'math.h' file not found
    5 | #include <math.h>
      |          ^~~~~~~~
1 error generated.
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck --allow-unused-prefixes /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/123867