[clang] [CIR] Add codegen for atomic fence builtin with non-const memory order (PR #172455)

[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/43188

<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 :: Semantics/modfile72.f90 (4054 of 4065)
PASS: Flang :: Driver/target-cpu-features.f90 (4055 of 4065)
PASS: Flang :: Fir/target-rewrite-complex.fir (4056 of 4065)
PASS: Flang :: Transforms/stack-arrays.f90 (4057 of 4065)
PASS: Flang :: Semantics/numeric_storage_size.f90 (4058 of 4065)
PASS: Flang :: Driver/use-module-error.f90 (4059 of 4065)
PASS: Flang :: Transforms/OpenACC/acc-implicit-data-fortran.F90 (4060 of 4065)
PASS: Flang :: Lower/OpenMP/rtl-flags.f90 (4061 of 4065)
PASS: Flang :: Driver/linker-options.f90 (4062 of 4065)
PASS: Flang :: Driver/omp-driver-offload.f90 (4063 of 4065)
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=2776.917357

```

</details>

https://github.com/llvm/llvm-project/pull/172455