[llvm] [NFC] [IndVarSimplify] add overflowing tests (PR #159877)

[Florian Mayer via llvm-commits]

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@@ -232,11 +361,6 @@ for.body:                                         ; preds = %entry, %cont
 ; It is theoretically possible to prove this, but SCEV cannot
 ; represent non-unsigned-wrapping subtraction operations.
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fmayer wrote:

Changed to what I understood the comment to mean (because it refers to a quite ambiguous "this").

https://github.com/llvm/llvm-project/pull/159877