Bug #FX-175: Completed build options for Pthread API

The configuration script "AX_PTHREAD" was added to the build specification
so that corresponding special parameters will be taken into account.
http://www.gnu.org/software/autoconf-archive/ax_pthread.html

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge pull request #58 from elfring/Complete_build_options_for_Pthread_API2

Complete build options for Pthread API.