[llvm] [AArch64] Legalize fp128 scalars as libcalls for G_FCMP (PR #98452)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> As you are touching the legaliizer, a MIR test would be nice.

For the most part I think we should stop doing that unless there's a really special edge case involved that would be hard to reproduce. They're harder to maintain and can miss the system not working as a whole 

https://github.com/llvm/llvm-project/pull/98452