[llvm] ConstraintElim: add dry-run routine to fail early (PR #99670)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Compile-time impact on my [dataset](https://github.com/dtcxzyw/llvm-opt-benchmark):
```
Top 5 improvements:
  darktable/FujiDecompressor.cpp.ll 3874209532 3010886363 -22.28%
  faiss/IndexIVFAdditiveQuantizerFastScan.cpp.ll 874177979 821419686 -6.04%
  cmake/cmPolicies.cxx.ll 2196055101 2089770103 -4.84%
  php/metaphone.ll 3643053889 3480158718 -4.47%
  faiss/IndexHNSW.cpp.ll 2712011139 2615367204 -3.56%
Top 5 regressions:
  faiss/IndexFlat.cpp.ll 608107033 638979523 +5.08%
  faiss/IndexIVFFastScan.cpp.ll 7470109132 7751418757 +3.77%
  faiss/utils.cpp.ll 1280148979 1317007093 +2.88%
  lightgbm/dataset_loader.cpp.ll 7403066309 7608114932 +2.77%
  gromacs/freeenergydispatch.cpp.ll 724512915 744495719 +2.76%
Overall: 0.14623721%
```



https://github.com/llvm/llvm-project/pull/99670