Enable __gnat_alternate_stack for most linux

	* init.c [__linux__] (HAVE_GNAT_ALTERNATE_STACK): New define.
	(__gnat_alternate_stack): Enable for all linux except ia64.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@209653 138bc75d-0d04-0410-961f-82ee72b054a4
Add ada configuration for aarch64-linux

	* gcc-interface/Makefile.in: Support aarch64-linux.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@209654 138bc75d-0d04-0410-961f-82ee72b054a4