Complete build options for Pthread API

[Markus.Elfring@xxxxxx (Markus Elfring)]

Hello,

Would you like to add the configuration script "AX_PTHREAD" to your build
specification?
http://www.gnu.org/software/autoconf-archive/ax_pthread.html
http://trac.pjsip.org/repos/browser/pjproject/trunk/aconfigure.ac?rev=4435#L115

Regards,
Markus