[clang] [clang][Modules] Complete the implementation of P2615: Meaningful exports (PR #194201)

[Victor Chernyakin via cfe-commits]

================
@@ -440,6 +443,87 @@ Decl *Parser::ParseExportDeclaration() {
                                        T.getCloseLocation());
 }
 
+void Parser::CheckUnbracedLinkageOrExportDeclaration(
+    Decl *LinkageOrExportDecl) {
+  const auto *DC = cast<DeclContext>(LinkageOrExportDecl);
+  if (DC->decls_empty())
+    return;
----------------
localspook wrote:

That causes the following tests to fail:

```
CXX/module/module.interface/p2-2.cpp
CXX/module/module.interface/p3.cpp
CodeCompletion/keywords-cxx20.cpp
Modules/merge-concepts.cppm
```


https://github.com/llvm/llvm-project/pull/194201