Fix buildworld when cross-building and MK_INFO == yes
build-tools doesn't have consistent install logic, so to avoid disrupting that
I chose to move compiling texinfo from build-tools to bootstrap-tools. This is
a misnomer and I'd like to resolve that item sometime in the near future if
possible.
This commit adds a new knob, MK_INFO_SUPPORT, and builds texinfo depending on
whether or not that knob is set