[llvm] [MIR] Serialize virtual register flags (PR #110228)

[Matt Arsenault via llvm-commits]

================
@@ -127,6 +127,16 @@ bool PerTargetMIParsingState::getRegisterByName(StringRef RegName,
   return false;
 }
 
+bool PerTargetMIParsingState::getVRegFlagValue(StringRef FlagName,
+                                               uint8_t &FlagValue) const {
+  const auto *TRI = Subtarget.getRegisterInfo();
+  auto FV = TRI->getVRegFlagValue(FlagName);
+  if (!FV.has_value())
+    return true;
+  FlagValue = FV.value();
----------------
arsenm wrote:

```suggestion
  std::optional<uint8_t> FV = TRI->getVRegFlagValue(FlagName);
  if (!FV)
    return true;
  FlagValue = *FV;
```

https://github.com/llvm/llvm-project/pull/110228