Problem upgrading exim-mysql

[gcn53 at vfemail.net]

I'm running the exim-mysql package on FreeBSD 4.7 and using the deprecated
exiscan patch for virus scanning.

I am now trying to upgrade my exim installation from exim-mysql-4.20_1 to the
latest exim-mysql-4.21_1, so as to use the new exiscan-acl patch and make use
of the new exim 4.21 features.

I am using the command "portupgrade -v exim-mysql" to perform the upgrade but
get the following error:

======
/usr/local/lib/mysql/libmysqlclient.so: undefined reference to `uncompress'
/usr/local/lib/mysql/libmysqlclient.so: undefined reference to `compress'
*** Error code 1

Stop in /usr/ports/mail/exim-mysql/work/exim-4.21/build-FreeBSD-i386.
*** Error code 1

Stop in /usr/ports/mail/exim-mysql/work/exim-4.21.
*** Error code 1

Stop in /usr/ports/mail/exim-mysql.
** Command failed [exit code 1]: /usr/bin/script -qa /tmp/portupgrade15850.0 mak
e
** Fix the problem and try again.
======

Has anyone any ideas as to how I might "Fix the problem"?

TIA
Graeme