[clang-tidy]unused using decls only check cpp files (#77335)

Author: HerrCai0907

clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.h

@@ -26,6 +26,9 @@ class UnusedUsingDeclsCheck : public ClangTidyCheck {
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
   void onEndOfTranslationUnit() override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
 
 private:
   void removeFromFoundDecls(const Decl *D);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -382,7 +382,7 @@ Changes in existing checks
 
 - Improved :doc:`misc-unused-using-decls
   <clang-tidy/checks/misc/unused-using-decls>` check to avoid false positive when
-  using in elaborated type.
+  using in elaborated type and only check cpp files.
 
 - Improved :doc:`modernize-avoid-bind
   <clang-tidy/checks/modernize/avoid-bind>` check to