[llvm] [SimplifyCFG] Reuse function comdat for switch lookup table (PR #190995)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

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

Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/42699

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

```
Step 6 (test-build-check-mlir-build-only-check-mlir) failure: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
...
PASS: MLIR :: Pass/pipeline-options-parsing.mlir (4022 of 4032)
PASS: MLIR-Unit :: IR/./MLIRIRTests/40/148 (4023 of 4032)
PASS: MLIR-Unit :: Pass/./MLIRPassTests/11/14 (4024 of 4032)
PASS: MLIR-Unit :: IR/./MLIRIRTests/1/148 (4025 of 4032)
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/11/30 (4026 of 4032)
PASS: MLIR :: mlir-runner/utils.mlir (4027 of 4032)
PASS: MLIR :: mlir-tblgen/rewriter-errors.td (4028 of 4032)
PASS: MLIR :: mlir-reduce/opt-reduction/cse-test.mlir (4029 of 4032)
PASS: MLIR :: mlir-reduce/opt-reduction/dce-test.mlir (4030 of 4032)
PASS: MLIR :: mlir-tblgen/op-error.td (4031 of 4032)
command timed out: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2717.586343

```

</details>

https://github.com/llvm/llvm-project/pull/190995