libc: io: implement file io buffering and internal locking for concurrency

lib/libc/io/stdio/fclose.c

@@ -15,10 +15,13 @@ int fclose(struct __opaque_file *stream)
 
 	close(stream->f_fd);
 
-	if (stream->f_buf) {
-		free(stream->f_buf);
+	if (stream->f_buf.buf_ptr) {
+		free(stream->f_buf.buf_ptr);
+	}
+
+	if (!(stream->f_flags & FILE_STATIC)) {
+		free(stream);
 	}
 
-	free(stream);
 	return SUCCESS;
 }