gthr-posix.h (__gthread_active_p): Use pthread_cancel instead of pthread_create to find out if threads are enabled.

	* gthr-posix.h (__gthread_active_p): Use pthread_cancel instead
	of pthread_create to find out if threads are enabled.
	* gthr-posix95.h (__gthread_active_p): Likewise.

From-SVN: r93762