[llvm] DAG: Avoid using getLibcallName when looking for a divrem call (PR #170413)

[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/34280

<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-Unit :: Dialect/OpenACC/./MLIROpenACCTests/35/60 (3708 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/54/60 (3709 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/10/60 (3710 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/9/60 (3711 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/30/60 (3712 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/56/60 (3713 of 3719)
PASS: MLIR :: mlir-tblgen/cpp-class-comments.td (3714 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/55/60 (3715 of 3719)
PASS: MLIR-Unit :: Dialect/OpenACC/./MLIROpenACCTests/44/60 (3716 of 3719)
PASS: MLIR :: mlir-reduce/dce-test.mlir (3717 of 3719)
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=1701.421365

```

</details>

https://github.com/llvm/llvm-project/pull/170413