[llvm] AMDGPU: Avoid report_fatal_error for reporting libcalls (PR #145134)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > but there is no test for that?
> 
> 
> 
> Ideally we should have one... But there was not one before too.

This isn't really supposed to happen in the first place so there isn't a reliable test. Would need to have a known broken operation 

https://github.com/llvm/llvm-project/pull/145134