[clang] [analyzer] Refactor recognition of the errno getter functions (PR #91531)

[Balázs Kéri via cfe-commits]

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@@ -74,9 +73,13 @@ REGISTER_TRAIT_WITH_PROGRAMSTATE(ErrnoRegion, const MemRegion *)
 
 REGISTER_TRAIT_WITH_PROGRAMSTATE(ErrnoState, errno_modeling::ErrnoCheckState)
 
-/// Search for a variable called "errno" in the AST.
-/// Return nullptr if not found.
-static const VarDecl *getErrnoVar(ASTContext &ACtx) {
+void ErrnoModeling::checkASTDecl(const TranslationUnitDecl *D,
+                                 AnalysisManager &Mgr, BugReporter &BR) const {
+  // Try to find the declaration of the external variable `int errno;`.
+  // There are also C library implementations, where the `errno` location is
+  // accessed via a function that returns its address; in those environments
+  // this callback does nothing.
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balazske wrote:

```suggestion
  // this callback has no effect.
```

https://github.com/llvm/llvm-project/pull/91531