[llvm] MCExpr-ify SIProgramInfo (PR #88257)

[Nico Weber via llvm-commits]

nico wrote:

A layering question: The new test heavily reaches into llvm/lib/Target/AMDGPU internals. Given that, why is it in unittests/MC/AMDGPU instead of unittests/Target/AMDGPU

https://github.com/llvm/llvm-project/pull/88257