Upgrade ConstantFP's negative zero and infinity getters to handle vector types.

Will be used soon.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199552 91177308-0d34-0410-b5e6-96231b3b80d8
InstCombine: Make the (fmul X, -1.0) -> (fsub -0.0, X) transform handle vectors too.

PR18532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199553 91177308-0d34-0410-b5e6-96231b3b80d8