Remove warnings on WIN32

src/file.c

@@ -0,0 +1,35 @@
+/*
+ *  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
+ */
+
+
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <gmssl/error.h>
+
+
+int file_size(FILE *fp, size_t *size)
+{
+	int fd;
+	struct stat st;
+
+#ifdef WIN32
+	fd = _fileno(fp);
+#else
+	fd = fileno(fp);
+#endif
+	if (fstat(fd, &st) < 0) {
+		error_print();
+		return -1;
+	}
+	*size = st.st_size;
+	return 1;
+}