freebsd 6.4 -> 7.3 upgrade failure, ports openssl, and libz.so.3 versus libz.so.4

[Benno Overeinder]

Hi,

I am upgrading a system from freebsd 6.4 to freebsd 7.3 from source. On
this system, the ports openssl package has been installed.

With the make buildworld, the compilation of sendmail fails with the
message:
/usr/obj/usr/src/tmp/usr/bin/ld: warning: libz.so.3, needed by
/usr/local/lib/libssl.so, not found (try using -rpath or -rpath-link)

Problem is that the new kernel is expecting (or compiling the sources
against) libz.so.4 (/usr/obj/usr/src/lib/libz/libz.so.4).  libz.so.3 is
available in /lib/libz.so.3 (FreeBSD 6.4).

Is there any way to break this dependency, such that the make buildworld
completes successfully?  It is openssl from ports depending on libz.so.3
of FreeBSD 6.4, sendmail is compiled with openssl from ports for FreeBSD
7.3, which provides libz.so.4...  The upgrade path 6.4 -> 7.3 with ports
openssl is probably not unique, others will have a similar upgrade path.

Can I specify something (/etc/make.conf?) such that 'make buildworld'
makes use of base openssl and not ports openssl?  Or should I uninstall
ports openssl (and recompile half of my ports, and later again recompile
all for freebsd 7.3)?

Any suggestions are welcome.

Thanks,

-- Benno