Add makewhatis to ITOOLS if MK_MAN != no

This will fix installation with differing host targets in installworld, so
one can build i386/i386 on an amd64 host, then install to an i386/i386 target

Reported by: alfred
Phabric: D1280
MFC after: 1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275622 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f