[llvm] X86: Fix asserting on bfloat argument/return without sse2 (PR #93146)

[Phoebe Wang via llvm-commits]

https://github.com/phoebewang commented:

In general, I think what we do here is useless. But I'm neutral to land it or not. I'll leave it to other reviewers.

https://github.com/llvm/llvm-project/pull/93146