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

[weiwei chen via llvm-commits]

weiweichen 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 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.

My PR is not really touch much ownership but more like fixing a dangerous existing bug. I don't disagree that it worthwhile reconsidering the actual ownership of the design, again, it's out of the scope of this bug fixing PR IMO, and I don't feel comfortable to moving ahead without understanding the context of the original design. Also, for API change and design change like this, should there be an RFC to get community inputs before moving forward? 

Can we please fix the bug first and then the design? Do they have to be done all in one go? It gets a bit frustrating here to be honest.

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