Changed IRBuilder::CreateZExtOrTrunc and IRBuilder::CreateSExtOrTrunc so they also work with vectors.

I also changed the name of a variable in IRBuilder::CreateFPExtOrFPTrunc to
match the names used in its two matching brethern as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172967 91177308-0d34-0410-b5e6-96231b3b80d8