Add set/get/endfsent() support for musl libc

This patch adds support for the following /etc/fstab API's on systems
that do not have them, e.g. musl libc on Alpine Linux.

- setfsent()
- getfsent(), and
- endfsent()

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

finit.c

@@ -27,7 +27,9 @@
 #include <ctype.h>
 #include <glob.h>
 #include <dirent.h>
+#ifdef HAVE_FSTAB_H
 #include <fstab.h>
+#endif
 #include <mntent.h>
 #include <sys/mount.h>
 #include <sys/stat.h>		/* umask(), mkdir() */