[InstCombine] reduce or-xor-or patterns

(A | ?) | (A ^ B) --> (A | ?) | B
https://alive2.llvm.org/ce/z/dbNQw4

This extends the existing transform to peek through
another 'or' instruction for the common operand.

This is the underlying missing fold that should allow
issue #56711 and issue #57120 to reduce even more.