1. Remove all the special handling of variables (-d -p -P -s -S) that
were dealing with DBG (-d) LDSTATIC/NOPIE (-p), and the rest with
disabling/enabling sanitizers.
2. Use emalloc/estrdup for all the allocators instead of only some cases.
3. Add -V varspec which passes variables on the command line (as DBG
and LDSTATIC used to be passed before) instead of appending them
to the on-the-fly Makefile using -v varspec.
4. Change the distrib and rescue Makefiles to use -V instead of the removed
flags.

The motivation of this is to make variable handling consistent, less magical,
and remove the need for changing crunchgen each time we want to add disabling
an option by default.

(as proposed in tech-toolchain)

branches: 1.13.12;
+= for MAKEFS_FLAGS

branches: 1.12.6; 1.12.10;
Don't set -mmultiple or -mno-string for PowerPC, the difference is too
small to really matter and it sometimes even increases the size.

branches: 1.11.2; 1.11.10;
Change all install media to use ipty instead of pty0

Fix build failure. Remove unknown device ttyv0.

branches: 1.9.6; 1.9.8;
Remove terminfo.db as it's now embedded in libterminfo.

Use the rescue terminfo.db in our images instead of termcap.

Replace references to local and now no-longer-existing termcap files
with references to ${DISTRIBB}/common/termcap. Hi, abs@!

Ten identical list.inet6 files, or one common/list.inet6?
Not a difficult choice.

${NETBSDSRCDIR}/distrib/common/protocols => ${DISTRIBDIR}/common/protocols
${NETBSDSRCDIR}/distrib/common/services => ${DISTRIBDIR}/common/services

Use the cutdown distrib/common/services and distrib/common/protocols
rather than the full fat etc versions

branches: 1.3.12;
Since /etc/services has gotten rather large, use a minimal one for install
kernels. (mount_nfs is notably the only binary that doesn't gracefully deal
with the lack of an /etc/services file, it appears.)

Only use ping6 and rtsol if ${USE_INET6} != "no".
Part of PR 28994.

NWDO for ibmnws.