feat: add gmssl headers

include/gmssl/api.h

@@ -0,0 +1,22 @@
+/*
+ *  Copyright 2014-2023 The GmSSL Project. All Rights Reserved.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the License); you may
+ *  not use this file except in compliance with the License.
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ */
+
+#ifndef GMSSL_API_H
+#define GMSSL_API_H
+
+
+#ifdef WIN32
+#define _gmssl_export  __declspec(dllexport)
+#else
+// use -fvisibility=hidden to change the "default" behavior
+#define _gmssl_export  __attribute__((visibility("default")))
+#endif
+
+
+#endif