Use JUMPTARGET in x86-64 pthread

When PLT may be used, JUMPTARGET should be used instead calling the
function directly.

	* sysdeps/unix/sysv/linux/x86_64/cancellation.S
	(__pthread_enable_asynccancel): Use JUMPTARGET to call
	__pthread_unwind.
	* sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S
	(__condvar_cleanup2): Use JUMPTARGET to call _Unwind_Resume.
	* sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S
	(__condvar_cleanup1): Likewise.