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

[Shilei Tian via llvm-commits]

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@@ -0,0 +1,98 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
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shiltian wrote:

like this? it doesn't seem to be able to reproduce the issue.

```
define void @test(ptr %p, i32 %a, i32 %b) {
  %mul = mul i32 %a, %b
  %lshr = lshr i32 %mul, 16
  store i32 %lshr, ptr %p, align 4
  ret void
}
```

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