From Lua 5.2: debug.setmetatable() returns object.

Needs -DLUAJIT_ENABLE_LUA52COMPAT.

src/lib_debug.c

@@ -41,7 +41,9 @@ LJLIB_CF(debug_setmetatable)
   lj_lib_checktabornil(L, 2);
   L->top = L->base+2;
   lua_setmetatable(L, 1);
+#if !LJ_52
   setboolV(L->top-1, 1);
+#endif
   return 1;
 }