[Intrinsic] Signed Saturation Addition Intrinsic

Add an intrinsic that takes 2 integers and perform saturation addition on them.

This is a part of implementing fixed point arithmetic in clang where some of
the more complex operations will be implemented as intrinsics.

Differential Revision: https://reviews.llvm.org/D53053

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344629 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed