MFH: r468557

Correctly link to MIT KRB5 libraries when selected.

This was discovered while working through issues relating to an
exp-run using base with private Heimdal, part of the project to
make a) Heimdal in base private and b) import MIT into base (PR 222745).

PR:		227680
Submitted by:	cy@
Approved by:	Corey Halpin <chalpin@cs.wisc.edu> (maintainer)
Approved by:	portmgr (riggs)