[DAGCombiner] Reassociate the operands from (OR (OR(CMP1, CMP2)), CMP3) to (OR...

[DAGCombiner] Reassociate the operands from (OR (OR(CMP1, CMP2)), CMP3) to (OR (OR(CMP1, CMP3)), CMP2)

This happens when CMP1 and CMP3 have the same predicate (or CMP2 and CMP3 have
the same predicate).

This helps optimizations such as the fololowing one:
CMP(A,C)||CMP(B,C) => CMP(MIN/MAX(A,B), C)
CMP(A,C)&&CMP(B,C) => CMP(MIN/MAX(A,B), C)

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D156215