PHP and MySQL compile and install fine, but Apache exits with no error codes in this configuration. I have put Apache in debug mode and it still exits with no error codes! When I remove the PHP module, Apache starts fine. PHP works fine on the command line. MySQL fine works on the command line.
I had exactly this problem in OpenBSD 3.7, when using PHP (both 4.4 and 5.0.x) and MySQL 4.1.x. Apache simply didn't start, but gave no error message at all. If I disabled PHP, it did start. I thought it was PHP, so fiddled around with options, versions and so on, and nothing helped.
Downgrading to MySQL 4.0.x (the version in the ports, in fact) and recompiling PHP (any version) solved the problem.