Fix to build with musl profile
Fix by David Denoncin
https://bugs.gentoo.org/715712

--- a/unix/unix.c    2020-07-24 17:02:06.056825906 +0200
+++ b/unix/unix.c 2020-07-24 17:02:22.483491781 +0200
@@ -13,6 +13,7 @@
 #include <sys/stat.h>
 #include <string.h>
 #include <ctype.h>
+#include <fcntl.h>
 #include "port.h"

 int iocount;