[clang] [clang] Disambiguate GMF internal functions across partitions (PR #219238)

[Chuanqi Xu via cfe-commits]

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@@ -1110,9 +1110,34 @@ void CXXNameMangler::mangleNameWithAbiTags(
 }
 
 void CXXNameMangler::mangleModuleName(const NamedDecl *ND) {
-  if (ND->isExternallyVisible())
+  if (ND->isExternallyVisible()) {
     if (Module *M = ND->getOwningModuleForLinkage())
       mangleModuleNamePrefix(M->getPrimaryModuleInterfaceName());
+    return;
+  }
+
+  // A function with internal linkage in a global module fragment denotes a
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ChuanqiXu9 wrote:

We should add a FIXME that states the behavior is actually not conforming but our strategy for real world use cases. And it is better to introduce a flag for this so that users can control it.

https://github.com/llvm/llvm-project/pull/219238