Re-include the threads library, which had been coming in transitively through drakeCommon.
Re-include the threads library, which had been coming in transitively through drakeCommon.

sheim/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,sheim/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake,billhoffman/drake,billhoffman/drake