Mac OS X 10.1 development tools default to a two-level 
namespace, whereas 10.0 tools defaulted to a flat 
namespace. A discussion of this problem (and one solution, 
maybe) is posted on Mark Liyanage's site at 
http://www.entropy.ch/software/macosx/php/.

I used the trick explained here to get around a problem 
building where I got complaints that the -undefined flag 
used in the configure script was incorrect for two-level 
namespace.

However, when I try to use the --with-apxs flag with the 
configure script I still can't compile. I have been trying 
to build a shared object version of RC3 and I only get a 
little farther in the process until I get another error 
about multiply-defined symbols when linking libphp4.la.