Built-in function table sentinels do not need names

builtin.h

@@ -17,7 +17,7 @@ struct rb_builtin_function {
 };
 
 #define RB_BUILTIN_FUNCTION(_i, _name, _fname, _arity, _compiler) {\
-  .name = #_name, \
+  .name = _i < 0 ? NULL : #_name, \
   .func_ptr = (void *)_fname, \
   .argc = _arity, \
   .index = _i, \