Can't get PHP to load mongo.so extension

Question

I've tried building the library with PECL, I've tried downloading it from github. I've tried MAMP, I've tried XAMPP. I always get the same error:

PHP Warning: PHP Startup: Unable to load dynamic library '/Applications/XAMPP/xamppfiles/lib/php/php-5.3.1/extensions/no-debug-non-zts-20090626/mongo.so' - dlopen(/Applications/XAMPP/xamppfiles/lib/php/php-5.3.1/extensions/no-debug-non-zts-20090626/mongo.so, 9): no suitable image found. Did find:\n\t/Applications/XAMPP/xamppfiles/lib/php/php-5.3.1/extensions/no-debug-non-zts-20090626/mongo.so: unknown required load command 0x80000022 in Unknown on line 0

(Paths differ depending on XAMPP or MAMP)

I'm running OS 10.5.8. Any ideas?