[clang] [Clang] fix crash by avoiding invalidation of extern main declaration during strictness checks (PR #104594)

[via cfe-commits]

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@@ -78,12 +80,12 @@ namespace ns {
 extern "C" struct A { int main(); }; // ok
 
 namespace c {
-  extern "C" void main(); // expected-warning {{'main' should not be 'extern "C"'}}
+  extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
 }
 
 extern "C" {
   namespace Z {
-    void main(); // expected-warning {{'main' should not be 'extern "C"'}}
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cor3ntin wrote:

Yes - i think it's useful to test that `void main()` is recognized as a main function, albeit an invalid one

https://github.com/llvm/llvm-project/pull/104594