[clang] [Clang] strengthen checks for 'main' function to meet [basic.start.main] p2 requirements (PR #101853)

[via cfe-commits]

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@@ -2156,6 +2156,8 @@ class DeclContext {
     return getDeclKind() == Decl::TranslationUnit;
   }
 
+  bool isLinkageSpec() const { return getDeclKind() == Decl::LinkageSpec; }
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Sirraide wrote:

I don’t think we need this. The place where this is used can just do `isa<LinkageSpecDecl>(D)` or sth like that

https://github.com/llvm/llvm-project/pull/101853