Vectorize intrinsic math function calls in SLPVectorizer.
This patch adds support to recognize and vectorize intrinsic math functions in SLPVectorizer.
Review: http://reviews.llvm.org/D3560 and http://reviews.llvm.org/D3559


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207901 91177308-0d34-0410-b5e6-96231b3b80d8