[llvm] [X86][GlobalISel] Enable scalar versions of G_UITOFP and G_FPTOUI (PR #100079)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm I'm not sure if a new opcode is a good idea. x86 version clamps everything, that is out of bounds, to `80000000_00000000H`. So to make it work, we need to introduce an opcode for generic clamping to the specified value or values.

It is perfectly fine to define a new opcode with whatever the clamping behavior exists. I would suggest it's easier to just pattern match the explicit clamp code though 

https://github.com/llvm/llvm-project/pull/100079