[llvm] [CodeGen] Make MCContext in MachineModuleInfo a unique_ptr. (PR #104834)

[weiwei chen via llvm-commits]

weiweichen wrote:

> Is there any context actually using the move constructor?

I tried to remove the move constructor and compilation of llvm seems to be still fine with the projects that we are building, that is `mlir`, `clang`, `compiler-rt` and `lldb`.  So I guess it is not actually being used in the upstream repo and maybe some downstream projects are using this API (which we very much like to use it with the fix here for the Mojo compiler 😃 )

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