[llvm] [AMDGPU][GlobalISel] Allow bitcast of bf16 (PR #81674)

[Shilei Tian via llvm-commits]

shiltian wrote:

> It is there for a reason. You cannot really enable it without implementing global isel support for bf16. It will start failing silently. The point of this code to fail with an error. It will also start silently failing for multiple targets.

Okay. Then I'll disable the test in https://github.com/llvm/llvm-project/pull/80908 since it is not supported yet.

https://github.com/llvm/llvm-project/pull/81674