Adjust some checks missed in r274637, now that pi_rname can be NULL.

Additionally fix a misparenthesization in the same check, noticed while
fixing the first bug. This bug only appears to cause problems if the same
USDT probe appears twice within a static function.

X-MFC-With:	r274637


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275012 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Add definitions of kerberos libraries


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275014 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f