CustomLowerNode was not being called during SplitVectorOperand,
meaning custom legalization could not be used by targets.
This also adds a test case for NVPTX that depends on this custom
legalization.
Differential Revision: http://llvm-reviews.chandlerc.com/D1195
Attempt to fix the buildbots by making the X86 test I just added platform independent
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187202 91177308-0d34-0410-b5e6-96231b3b80d8