[InstCombine] Simplify the overflow result of `umulov X, X` (#80796)

This patch does the following folds if only the overflow result is used:
```
extractvalue (umul.with.overflow iN X, X), 1 -> icmp ugt X, 2^(N/2)-1
```
Alive2: https://alive2.llvm.org/ce/z/a8yPC6