Ensure that the makewhatis symlink is added in the bootstrap-tools stage

We currently set MK_MAN=no in $BSARGS so MK_MAN_UTILS will also be false
which means that the makewhatis symlink will not be created.
This change fixes the build when using both -DBUILD_WITH_STRICT_TMPPATH and
-DBOOTSTRAP_ALL_TOOLS.

Tested by: andrew
Differential Revision: https://reviews.freebsd.org/D16761