[clang] Adds a pseudonym to clang"s windows mangler... (PR #97792)

[Andrey Ali Khan Bolshakov via cfe-commits]

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@@ -1938,12 +1946,23 @@ void MicrosoftCXXNameMangler::mangleTemplateArgValue(QualType T,
         mangleNumber(V.getLValueOffset().getQuantity());
       } else if (!V.hasLValuePath()) {
         // FIXME: This can only happen as an extension. Invent a mangling.
-        break;
+        DiagnosticsEngine &Diags = Context.getDiags();
+        unsigned DiagID =
+            Diags.getCustomDiagID(DiagnosticsEngine::Error,
+                                  "cannot mangle this template argument yet "
+                                  "(non-null base with null lvalue path)");
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bolshakov-a wrote:

I think that "lvalue base" and "lvalue path" are clang internal terms. Not sure whether they are worth appearing in diagnostics.

https://github.com/llvm/llvm-project/pull/97792