[llvm] [AMDGPU][MC] Support UC_VERSION_* constants. (PR #95618)

[Ivan Kosarev via llvm-commits]

kosarev wrote:

> We want to do less work at parse time and postpone `evaluateAsRelocatableImpl` to object file generation time.

Is AMDGPU the only backend that has or needs that notion of constant symbols? I was rather expecting the common MC infrastructure to have a proper support for them at some point.

https://github.com/llvm/llvm-project/pull/95618