[clang] [clang] Support header shadowing diagnostics in Clang header search (PR #162491)

[Qiu Chaofan via cfe-commits]

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@@ -465,6 +465,12 @@ class HeaderSearch {
     ExternalSource = ES;
   }
 
+  void DiagnoseHeaderShadowing(
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ecnelises wrote:

nit: use small camel case for methods (https://llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly)

https://github.com/llvm/llvm-project/pull/162491