Codegen: Fix llvm.*absdiff semantic.

Fixes the overflow case of llvm.*absdiff intrinsic also updats the tests and LangRef.rst accordingly.

Differential Revision: http://reviews.llvm.org/D11678

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248483 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed