Turn into a const method.

Author: bwendling

clang/include/clang/Sema/Sema.h

@@ -2518,7 +2518,7 @@ class Sema final : public SemaBase {
 
   bool BuiltinNonDeterministicValue(CallExpr *TheCall);
 
-  bool IsBuiltinCountedByRef(const Expr *E) {
+  bool IsBuiltinCountedByRef(const Expr *E) const {
     const CallExpr *CE =
         E ? dyn_cast<CallExpr>(E->IgnoreParenImpCasts()) : nullptr;
     return CE && CE->getBuiltinCallee() == Builtin::BI__builtin_counted_by_ref;