Define _XOPEN_SOURCE when building to get crypt() from <unistd.h> instead of using <crypt.h> in sulogin.c, to get the source building with the musl C library.

src/Makefile

@@ -10,7 +10,7 @@
 
 CPPFLAGS =
 CFLAGS	?= -ansi -O2 -fomit-frame-pointer
-override CFLAGS += -W -Wall -D_GNU_SOURCE
+override CFLAGS += -W -Wall -D_XOPEN_SOURCE -D_GNU_SOURCE
 STATIC	=
 MANDB	:= s@^\('\\\\\"\)[^\*-]*-\*- coding: [^[:blank:]]\+ -\*-@\1@
 

src/sulogin.c

@@ -44,9 +44,6 @@
 #include <sys/ttydefaults.h>
 #include <errno.h>
 #include <sys/ioctl.h>
-#if defined(__GLIBC__)
-#  include <crypt.h>
-#endif
 #ifdef __linux__
 #  include <sys/statfs.h>
 #  include <sys/mount.h>