[llvm] [GlobalISel] Check whether `G_CTLZ` is legal in `matchUMulHToLShr` (PR #126457)

[Shilei Tian via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
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shiltian wrote:

There are two interesting things in this test case:

1. It is not reproducible w/o `-O0` argument
2. The `udiv` is actually a UB, and replacing either of its operand will make the crash go away (or the pattern not recognized such that the issue will not happen).

https://github.com/llvm/llvm-project/pull/126457