ia64: Fix thread stack allocation permission set (BZ #21672)

ia64: Fix thread stack allocation permission set (BZ #21672)

This patch fixes ia64 failures on thread exit by madvise the required
area taking in consideration its disjoing stacks
(NEED_SEPARATE_REGISTER_STACK).  Also the snippet that setup the
madvise call to advertise kernel the area won't be used anymore in
near future is reallocated in allocatestack.c (for consistency to
put all stack management function in one place).

Checked on x86_64-linux-gnu and i686-linux-gnu for sanity (since
it is not expected code changes for architecture that do not
define NEED_SEPARATE_REGISTER_STACK) and also got a report that
it fixes ia64-linux-gnu failures from Sergei Trofimovich
<slyfox@gentoo.org>.

	[BZ #21672]
	* nptl/allocatestack.c [_STACK_GROWS_DOWN] (setup_stack_prot):
	Set to use !NEED_SEPARATE_REGISTER_STACK as well.
	(advise_stack_range): New function.
	* nptl/pthread_create.c (START_THREAD_DEFN): Move logic to mark
	stack non required to advise_stack_range at allocatestack.c