[llvm] [CodeGen] Fix `MachineModuleInfo`'s move constructor to be more safe with `MCContext` ownership. (PR #104834)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I don't feel like object to what your intended design/improvement for this part, though that's really not what this PR is for and what the problem I'm trying to solve here. 

Your patch only is entirely about the ownership of MachineModuleInfo. Just trying to move along with something that happens to avoid your problem today without a real design decision being made is a path to the project bitrotting as a whole.

https://github.com/llvm/llvm-project/pull/104834