Add support for the Saturation Arithmetic Intrinsics (llvm.uadd.sat.* and others)

[zlfn]

It has already been reported in #111 that llvm.uadd.sat.* is not supported.
The instruction that needs to be implemented is as follows.

• llvm.uadd.sat.*
• llvm.usub.sat.*
• llvm.sadd.sat.*
• llvm.ssub.sat.*
• llvm.sshl.sat.*
• llvm.ushl.sat.*

I don't think it's going to be difficult to implement. I'll look at it later when I have time.