[clang] [Clang] strengthen checks for 'main' function to meet [basic.start.main] p3 requirements (PR #101853)

[via cfe-commits]

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@@ -7353,6 +7353,15 @@ void emitReadOnlyPlacementAttrWarning(Sema &S, const VarDecl *VD) {
   }
 }
 
+// Checks if VD is declared at global scope or with C language linkage
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Sirraide wrote:

```suggestion
// Checks if VD is declared at global scope or with C language linkage.
```
Extremely minor nit.

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