[clang] [flang] [llvm] [mlir] Make MMIWP not have ownership over MMI + Make MMI Only Use an External MCContext (PR #105541)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> @aeubanks @arsenm after looking into this in more detail, I realized that the `getContext` method of `MMI` is heavily used in the `AsmPrinter` to create symbols. Also not having it makes it harder for the `MMI` to create machine functions using `getOrCreateMachineFunction`.


The AsmPrinter is just an ordinary ModulePass. The initialization can just set a MMI member? 

https://github.com/llvm/llvm-project/pull/105541