When compiling PHP under Mac OS X, you currently must move the OS X port of libdl to libdl.a.old and libdl.dylib.old to prevent PHP from using them. Apache on Darwin/OS X already defines it's own version of the dlopen functions, and if PHP links against the libdl from the OS X dlcompat library, Apache will fail to run, complaining about multiple definitions of dlopen.

This may be more of an Apache issue than a PHP issue?
I haven't tried compiling Apache yet using dlcompat's libdl instead of it's built-in dlopen stuff, but I might try that just to see if it works.