[llvm] [Inline][Cloning] Defer constant propagation after phi-nodes resolution (PR #87963)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

@nikic, I confirm performing basic constant folding on average decreases the number of blocks being cloned; I think we should be more on track now (http://llvm-compile-time-tracker.com/compare.php?from=eec268e41000faad50b7bf977c9f1161e4006bab&to=65847e8c168123ad328683f96b1b37cd269ea85c&stat=instructions:u). I think we still want to do InstSimplify after cloning, since not doing it leads to regressions in stage2 scenario (http://llvm-compile-time-tracker.com/compare.php?from=60baaf153d05a7828b304050aba461ebb66232c6&to=78c72fd92fa1b22fd2d113bb4e821b484322aadd&stat=instructions:u), besides the following local failures:
```
********************
Failed Tests (8):
  LLVM :: DebugInfo/Generic/assignment-tracking/inline/shared-alloca.ll
  LLVM :: Transforms/Inline/byval.ll
  LLVM :: Transforms/Inline/inline_cleanup.ll
  LLVM :: Transforms/Inline/nonnull.ll
  LLVM :: Transforms/Inline/pr50270.ll
  LLVM :: Transforms/Inline/pr50589.ll
  LLVM :: Transforms/Inline/ptr-diff.ll
  LLVM :: Transforms/Inline/simplify-instruction-computeKnownFPClass-context.ll
```

https://github.com/llvm/llvm-project/pull/87963