Revert "Revert "cmake/pthread-config.cmake : use upstream FindThreads.cmake""
Revert "Revert "cmake/pthread-config.cmake : use upstream FindThreads.cmake""

This reverts commit 07f45288c5fb39a71f374eb4c6b42c8a42ec1847.

aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild