If after the compilation mod_wsgi on FreeBSD you are getting below message:

usr/local/apache2/modules/mod_wsgi.so: Undefined symbol "pthread_attr_init"

it means that you have to start you apache with some modyfication in dynamic linking, which simply saying is simply nothing more than set  environment variable like this:

LD_PRELOAD=/usr/lib/libc_r.so

In my case I put it into profile and shell rc files. Works perfectly.