Replying to ryandesign@…:
That user had installed a variety of ports without their required +darwin platform variants, and installed some others with improper +linux and +freebsd platform variants.
This analysis of that user's situation was incorrect; the "missing" +darwin variant was only an artifact of a bug in MacPorts 1.7.1 and earlier that did not properly record the +darwin variant in the registry.
I have now been able to reproduce the error in this ticket, and it is caused by simultaneously using both the +apache2 and +fastcgi variants of php5 when apache2 has been compiled with the +workermpm variant. I am marking this bug as a duplicate of #21281 because although that bug came later, it is not burdened by what we now know are irrelevant issues like this ticket is.