[MustExec][LICM] Handle latch being part of an inner cycle (PR57780)

[MustExec][LICM] Handle latch being part of an inner cycle (PR57780)

The algorithm in allLoopPathsLeadToBlock() does not handle the case
where the loop latch is part of the predecessor set correctly: In
this case, we may take the backedge (escaping to a different loop
iteration) and not execute other latch successors. This can happen
if the latch is part of an inner cycle.

Fixes https://github.com/llvm/llvm-project/issues/57780.

Differential Revision: https://reviews.llvm.org/D134279