[clang] [clang-tools-extra] [clang] improve class type sugar preservation in pointers to members (PR #130537)

[Erich Keane via cfe-commits]

================
@@ -13461,13 +13486,112 @@ static ElaboratedTypeKeyword getCommonTypeKeyword(const T *X, const T *Y) {
                                             : ElaboratedTypeKeyword::None;
 }
 
+static NestedNameSpecifier *getCommonNNS(ASTContext &Ctx,
+                                         NestedNameSpecifier *X,
+                                         NestedNameSpecifier *Y, bool Sugar) {
+  if (X == Y)
+    return X;
+
+  NestedNameSpecifier *Canon = Ctx.getCanonicalNestedNameSpecifier(X);
+  if (Canon != Ctx.getCanonicalNestedNameSpecifier(Y)) {
+    if (Sugar)
+      return nullptr;
+    llvm_unreachable("Should be the same NestedNameSpecifier");
+  }
+
+  NestedNameSpecifier *R;
----------------
erichkeane wrote:

```suggestion
  NestedNameSpecifier *R = nullptr;
```

https://github.com/llvm/llvm-project/pull/130537