Support emit specified custom sections into AoT file (#1207)

And add API to get the content of custom section with
section name for both wasm file and aot file.

core/config.h

@@ -168,6 +168,11 @@
 #define WASM_ENABLE_DEBUG_AOT 0
 #endif
 
+/* Custom sections */
+#ifndef WASM_ENABLE_LOAD_CUSTOM_SECTION
+#define WASM_ENABLE_LOAD_CUSTOM_SECTION 0
+#endif
+
 /* WASM log system */
 #ifndef WASM_ENABLE_LOG
 #define WASM_ENABLE_LOG 1