Strength reduce intrinsics with overflow into regular arithmetic operations if possible.

Strength reduce intrinsics with overflow into regular arithmetic operations if possible.

Some intrinsics, like s/uadd.with.overflow and umul.with.overflow, are already strength reduced.
This change adds other arithmetic intrinsics: s/usub.with.overflow, smul.with.overflow.
It completes the work on PR20194.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224417 91177308-0d34-0410-b5e6-96231b3b80d8