[llvm] [NFC][AMDGPU] Do not flush after printing every instruction (PR #95237)

[Ivan Kosarev via llvm-commits]

kosarev wrote:

> You can redirect stderr to a temp file and then just have another FileCheck run

Easy, but probably not ideal from performance and disk wearing perspectives.

> > I don't see how this resolves the problem. Given two streams are getting flushed interleaved at random points, it's not even guaranteed that the combined output contains complete lines. Also not going to work where check lines match both stdout and stderr and thus expect them to come in a particular order.
> 
> It resolves the problem because checking stderr/stdout being interleaved isn't a particularly good idea, IMO.

So it's necessary to update the tests that employ that then.

https://github.com/llvm/llvm-project/pull/95237