ports without configure do not receive CC

[[LoN]Kamikaze]

Ports that do not set CC in their configure target don't get informed about the value of CC because it is only appended to MAKE_ENV for the configure target. Therefore I have written this patch:

http://www.freebsd.org/cgi/query-pr.cgi?pr=101120

It appends CC and CXX to the MAKE_ENV for the build target if not configure target is present.

A port affected by the addressed problem is graphics/png. If anyone else thinks this problem should be addressed, please reply here.