MFC r316579

makefs: use emalloc and friends

The emalloc set of error-checking memory allocation routines were added
to libnetbsd in r316572. Use them in makefs to reduce differences with
NetBSD.

NetBSD revs:
cd9660.c 1.39
ffs.c 1.56
makefs.c 1.42
walk.c 1.27
cd9660/cd9660_archimedes.c 1.2
cd9660/cd9660_eltorito.c 1.20
cd9660/cd9660_write.c 1.16
cd9660/iso9660_rrip.c 1.12
ffs/buf.c 1.17
ffs/mkfs.c 1.26

Sponsored by: iXsystems, Inc.