Remove warnings on WIN32

include/gmssl/file.h

@@ -0,0 +1,27 @@
+/*
+ *  Copyright 2014-2022 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_FILE_H
+#define GMSSL_FILE_H
+
+#include <stdio.h>
+#include <string.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+int file_size(FILE *fp, size_t *size);
+
+
+#ifdef __cplusplus
+}
+#endif
+#endif