Merge branch 'feature/add_header_file_un_h' into 'master'

newlib: add "sys/un.h" header file

See merge request sdk/ESP8266_RTOS_SDK!1271

Author: donghengqaz

components/newlib/newlib/port/include/sys/un.h

@@ -0,0 +1,22 @@
+// Copyright 2020 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#define	AF_UNIX		1		/* local to host (pipes) */
+
+struct sockaddr_un {
+            short                    sun_family;                /*AF_UNIX*/
+            char                     sun_path[108];             /*path name */
+};