[llvm] [MacroFusion] Support commutable instructions (PR #82751)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I added a `IsCommutable` to control the generation of checking commutable operands, because we may not need it in all cases. @arsenm WDYT?

Wouldn't that be implied by the opcode in the first place? The instruction will already have isCommutable set 

https://github.com/llvm/llvm-project/pull/82751