[llvm] [LoopIdiom] Do not emit wcslen for underaligned wide loads (PR #216080)

[Henry Jiang via llvm-commits]

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

It might be a good idea to add a case where the `wchar_t` load is under aligned, but the indvar is known to be minimum ABI size aligned, to catch the other arm.

https://github.com/llvm/llvm-project/pull/216080