[llvm] [AMDGPU][MC] Allow UC_VERSION_* constant reuse (PR #96461)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > can you add a test for the user redefined case
> 
> This might be difficult. The main issue we are seeing right now is a tool that ends up initializing multiple disassembler instance on the same context. We can probably replicate this in a unit test if necessary.

Wouldn't this be just .set UC_VERSION_something something in an assembler file? 

https://github.com/llvm/llvm-project/pull/96461