[llvm] [CodeGen] Use first EHLabel as a stop gate for live range shrinking (PR #114195)

[via llvm-commits]

MuellerMP wrote:

Updated the patch to deal with rebuilds of the InstructionOrderMap (triggered an assertion during my tests).
I now use the same method the original author used for code motion barriers related to instruction with side effects:
Rebuilding the InstructionOrderMap so illegal code motion insertion points can't be referenced with FindDominatedInstruction.

https://github.com/llvm/llvm-project/pull/114195