Build full mandoc.db(5) databases by default using makewhatis(8)

Build full mandoc.db(5) databases by default using makewhatis(8)
without -Q during the build and in weekly(8).  According to tests
by many developers, makewhatis(8) takes a few minutes at most even
on slower hardware like octeon, loongson, ALIX, RPI3, Soekris,
cubox, softiron etc., and security(8) is often worse than makewhatis(8).

In case this causes excessive weekly(8) run times on even slower
(~50 MHz-class) CPUs, consider adding "MAKEWHATISARGS=-Q" to
/etc/weekly.local on machines that feel unhappy.

OK sthen@ kettenis@ millert@ deraadt@