bootstrap: Fix old boostrapping issue once and for all.

bootstrap: Fix old boostrapping issue once and for all.

This was fallout after iconv() removal of 'const' attribute to conform
with POSIX. All the later hacks are starting to accumulate and prevent
easy further base system upgrading. So given that main issue is c++
specific and only needed for bootstraping process deal with it straight
and remove all hacks(include shoehornings) that were caused by it.

To fix bootstrapping problems add WORLD_VERSION variable that indicates
current DragonFly base version and could be used to retrospectively
help bootstrapping from older releases. Makefile changes that depend on
WORLD_VERSION should *only* be used as a once switch and during native
compilations should *not* change default world makefiles logic.