Revert "[IRBuilder] Update IRBuilder::CreateFNeg(...) to return a UnaryOperator"

This reverts commit r374240. It broke OCaml tests:
http://lab.llvm.org:8011/builders/clang-x86_64-debian-fast/builds/19014

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374354 91177308-0d34-0410-b5e6-96231b3b80d8
20 files changed