Adjust included headers to be compatible with the musl C library. Patch from Matias A. Fonzo and Dragora.

src/ifdown.c

@@ -26,11 +26,11 @@ char *v_ifdown = "@(#)ifdown.c  1.11  02-Jun-1998  miquels@cistron.nl";
 #include <unistd.h>
 #include <time.h>
 #include <string.h>
+#include <errno.h>
 
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <sys/time.h>
-#include <sys/errno.h>
 
 #include <net/if.h>
 #include <netinet/in.h>

src/init.c

@@ -49,6 +49,7 @@
 #include <utmp.h>
 #include <ctype.h>
 #include <stdarg.h>
+#include <sys/ttydefaults.h>
 #include <sys/syslog.h>
 #include <sys/time.h>