[InstCombine] Add simplifications for div/rem with `i1` operands; PR62607

This is generally handled already in early CSE.

If a specialized pipeline is used, however, its possible for `i1`
operand with known-zero denominator to slip through. Generally the
known-zero denominator is caught and poison is returned, but if it is
indirect enough (known zero through a phi node) we can miss this case
in `InstructionSimplify` and then miss handling `i1`. This is because
`i1` is current handled with the following check:
    `if(Known.countMinLeadingZeros() == Known.getBitWidth() - 1)`

which only works on the assumption we don't know the denominator to be
zero. If we know the denominator to be zero, this check fails:
https://github.com/llvm/llvm-project/issues/62607

This patch simply adds an explicit `if(Known.isZero) return poison;`
which fixes the issue.

Alive2 Link for tests:
    https://alive2.llvm.org/ce/z/VTw54n

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D150142