Fix duplicate code in ConstantFolding

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202913 91177308-0d34-0410-b5e6-96231b3b80d8
Allow constant folding of fma and fmuladd

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202914 91177308-0d34-0410-b5e6-96231b3b80d8