message: [ExpressionParser] Prefer isa<> to dyn_cast<>. NFCI.
  The result type is unused anyway.
diff: @@ -2015,8 +2015,7 @@ void ClangExpressionDeclMap::AddOneFunction(NameSearchContext &context,
  if (!extern_c) {
  TypeSystem *type_system = function->GetDeclContext().GetTypeSystem();
  - if (ClangASTContext *src_ast =
  - llvm::dyn_cast<ClangASTContext>(type_system)) {
  + if (llvm::isa<ClangASTContext>(type_system)) {
  clang::DeclContext *src_decl_context =
  (clang::DeclContext *)function->GetDeclContext()
  .GetOpaqueDeclContext();
  