[DAGCombiner] Generalize FADD constant combines to work with vectors

Updated the FADD combines to work with vectors as well as scalars.

Differential Revision: http://reviews.llvm.org/D13416

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249251 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed