feat(esp8266): Add WIFI socket and async APIs

1. add section to linking file

components/esp8266/include/esp_module.h

@@ -0,0 +1,38 @@
+// Copyright 2018 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.
+
+#ifndef _ESP_MODULE_H
+#define _ESP_MODULE_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define __EXPORT_SYMBOL_NAME(sec) "ksymatab"sec
+
+#define __EXPORT_SYMBOL(sym, sec)                       \
+    static const typeof(sym) *__ksymtab_##sym           \
+       __attribute__((used,section("ksymatab"sec)))     \
+       = &sym
+
+#define __DECLARE_SYMBOL_NAME(sec) __EXPORT_SYMBOL_NAME(sec)
+
+#define __DECLARE_SYMBOL(type, sym, sec)                \
+    static const type sym __attribute__((used,section("ksymatab"sec),aligned(sizeof(void *))))
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _ESP_MODULE_H */