To follow up on my own post I did a quick grep on files in the src
directory containing mktemp lines:

dist/bind/bin/nslookup/list.c
distrib/notes/common/main
distrib/sets/lists/base/mi
distrib/sets/lists/comp/mi
distrib/sets/lists/man/mi
domestic/include/kerberosIV/protos.h
domestic/usr.sbin/kprop/kprop.c
gnu/dist/binutils/bucomm.c
gnu/dist/gcc/choose-temp.c
gnu/dist/gcc/collect2.c
gnu/dist/gcc/config/alpha/xm-winnt.h
gnu/dist/gcc/config/i386/xm-os2.h
gnu/dist/gcc/config/mips/mips.c
gnu/dist/gcc/config/xm-lynx.h
gnu/dist/gcc/gcc.c
gnu/dist/gcc/gcc.cps
gnu/dist/gcc/gcc.texi
gnu/dist/gcc/mips-tfile.c
gnu/dist/gcc/sys-protos.h
gnu/dist/gdb/remote-nindy.c
gnu/dist/libf2c/changes.netlib
gnu/dist/libf2c/libI77/README.netlib
gnu/dist/libf2c/libI77/Version.c
gnu/dist/libf2c/libI77/open.c
gnu/dist/libf2c/libI77/rawio.h
gnu/dist/libf2c/readme.netlib
gnu/dist/libiberty/choose-temp.c
gnu/dist/texinfo/util/texindex.c
gnu/lib/libg2c/obj/Version_I.c
gnu/lib/libg2c/obj/open_I.c
gnu/usr.bin/gas/input-file.c
gnu/usr.bin/gawk/NEWS
gnu/usr.bin/groff/ChangeLog
gnu/usr.bin/groff/indxbib/indxbib.cc
gnu/usr.bin/groff/libgroff/tmpfile.cc
gnu/usr.bin/groff/xditview/Dvi.c
gnu/usr.bin/rcs/lib/conf.h
gnu/usr.bin/rcs/lib/rcsedit.c
gnu/usr.bin/rcs/lib/rcsfnms.c
include/stdlib.h
lib/libc/stdio/CVS/Entries
lib/libc/stdio/Makefile.inc
lib/libc/stdio/gettemp.c
lib/libc/stdio/mkdtemp.c
lib/libc/stdio/mkstemp.c
lib/libc/stdio/mktemp.3
lib/libc/stdio/mktemp.c
lib/libc/stdio/stdio.3
lib/libc/stdio/tmpnam.3
libexec/ftpd/ftpd.c
libexec/ftpd/ftpd.c.orig
sbin/mount_portal/mount_portal.c
sbin/restore/restore.8
share/man/man0/man3
share/man/tools/newsp.errs
share/man/tools/sp.ignore
usr.bin/CVS/Entries
usr.bin/Makefile
usr.bin/m4/eval.c
usr.bin/m4/main.c
usr.bin/man/man.conf.5
usr.bin/mktemp/CVS/Entries
usr.bin/mktemp/CVS/Repository
usr.bin/mktemp/Makefile
usr.bin/mktemp/mktemp.1
usr.bin/mktemp/mktemp.c
usr.bin/msgs/msgs.c
usr.bin/rdist/main.c
usr.bin/tn3270/sys_curses/system.c
usr.bin/window/wwterminfo.c
usr.bin/xlint/xlint/xlint.c
usr.bin/xstr/xstr.c
usr.bin/log.core
usr.sbin/amd/doc/am-utils.texi
usr.sbin/amd/doc/hlfsd.ps
usr.sbin/amd/hlfsd/homedir.c
usr.sbin/amd/mk-amd-map/mk-amd-map.c
usr.sbin/dhcp/client/dhclient.c
usr.sbin/lpr/lpd/printjob.c
usr.sbin/pkg_install/add/pkg_add.1
usr.sbin/pkg_install/create/pkg_create.1
usr.sbin/pkg_install/delete/pkg_delete.1
usr.sbin/pkg_install/info/pkg_info.1
usr.sbin/pkg_install/lib/pen.c
usr.sbin/sendmail/mail.local/mail.local.c
usr.sbin/sup/source/libc.h
usr.sbin/xntp/include/config.h
usr.sbin/xntp/include/l_stdlib.h
usr.sbin/xntp/include/ntp_machine.h
usr.sbin/xntp/xntp2netbsd
usr.sbin/xntp/xntpd/ntp_config.c
usr.sbin/ypserv/makedbm/makedbm.c
usr.sbin/ypserv/mkalias/mkalias.c
usr.sbin/ypserv/ypxfr/ypxfr.c

later,
T@W