Add ignore_enviroment attribute to sys.flags

Pyston already has Py_IgnoreEnvironmentFlag, just add it to sys.flags.

src/runtime/builtin_modules/sys.cpp

@@ -816,6 +816,8 @@ void setupSys() {
     sys_flags_cls->giveAttr(
         "__new__", new BoxedFunction(FunctionMetadata::create((void*)BoxedSysFlags::__new__, UNKNOWN, 1, true, true)));
     sys_flags_cls->tp_dealloc = (destructor)BoxedSysFlags::dealloc;
+
+    sys_flags_cls->giveAttr("ignore_environment", boxInt(Py_IgnoreEnvironmentFlag));
 #define ADD(name) sys_flags_cls->giveAttrMember(STRINGIFY(name), T_OBJECT, offsetof(BoxedSysFlags, name));
     ADD(division_warning);
     ADD(bytes_warning);