[llvm] [MIR] Save internal VirtRegMap state in MIR (PR #197361)

[Matt Arsenault via llvm-commits]

================
@@ -129,6 +129,16 @@ struct LLVM_ABI MachineFunctionInfo {
       const {
     return nullptr;
   }
+
+  // Placeholder for deserialization of the VirtRegMap object.
+  // This gets populuated by the MIRParser when the information is present
----------------
arsenm wrote:

```suggestion
  // This gets populated by the MIRParser when the information is present
```

https://github.com/llvm/llvm-project/pull/197361