These instructions assume that you have a working Apache 2.2 / PHP 5.3 in place and want to add the php mcrypt module. It will work as a fresh install, but keep in mind that additional configuration steps after these instructions are necessary to get your webserver working properly. Those additional steps are omitted here, as there are countless resources available on the Internet.
1. If you don’t already have the mcrypt module (in /usr/lib), download the libmcrypt source code from sourceforge here. Then extract the downloaded file in a Terminal and move inside the created directory. (cd libmcrypt-2.5.8 in my case)
2. Execute the following lines in one command in your Terminal, if you have a 64bit version of Apache/PHP:
CFLAGS=”-arch x86_64″ \
CXXFLAGS=”-arch x86_64″ \
./configure –disable-posix-threads
(for 32 bit versions: ./configure –disable-posix-threads)