[clang] [clang-cl] Fix value of __FUNCTION__ in MSVC mode. (PR #84014)

[Aaron Ballman via cfe-commits]

================
@@ -679,6 +679,19 @@ static void printExplicitSpecifier(ExplicitSpecifier ES, llvm::raw_ostream &Out,
   Out << Proto;
 }
 
+static void AddPrefix(PrintingPolicy &Policy, QualType T,
+                      llvm::raw_ostream &Out) {
+  if (!Policy.SuppressTagKeyword && Policy.SuppressScope &&
+      !Policy.SuppressUnwrittenScope) {
+    StringRef prefix;
+    prefix = T->isClassType()       ? "class "
+             : T->isStructureType() ? "struct "
+             : T->isUnionType()     ? "union "
+                                    : "";
+    Out << prefix;
----------------
AaronBallman wrote:

```suggestion
    StringRef prefix = T->isClassType()       ? "class "
             : T->isStructureType() ? "struct "
             : T->isUnionType()     ? "union "
                                    : "";
    Out << prefix;
```
And probably needs to be reformatted.

https://github.com/llvm/llvm-project/pull/84014