[DAGCombine] SimplifyNodeWithTwoResults - ensure same legalization for LO/HI operands (PR21207)
[DAGCombine] SimplifyNodeWithTwoResults - ensure same legalization for LO/HI operands (PR21207)

Consistently use (!LegalOperations || isOperationLegalOrCustom) for all node pairs.

Differential Revision: https://reviews.llvm.org/D53478

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@347255 91177308-0d34-0410-b5e6-96231b3b80d8

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