This patch add coredump support for the new "pauth" feature.  A few necessary
low level methods and descriptions are added accordingly.

2017-08-09  Jiong Wang  <jiong.wang@arm.com>
bfd/
	* elf-bfd.h (elfcore_write_aarch_pauth): New function declaration.
	* elf.c (elfcore_grok_aarch_pauth): New function.
	(elfcore_grok_note): Handle NT_ARM_PAUTH.
	(elfcore_write_aarch_pauth): New function.
	(elfcore_write_register_note): Handle ".reg-aarch-pauth" section.

gdb/
	* aarch64-linux-tdep.c: #include "auxv.h".
	#include "elf/common.h"
	(aarch64_collect_pauth_regset): New function.
	(aarch64_supply_pauth_regset): New function.
	(aarch64_linux_pauthregset): New regset.
	(aarch64_linux_iterate_over_regset_sections): Support
	".reg-aarch64-pauth" section.
	(aarch64_linux_core_read_description): New function.
	(aarch64_linux_init_abi): Register core_read_description method.
	* aarch64-linux-tdep.h (AARCH64_LINUX_SIZEOF_PAUTH): New define.
	(HWCAP_APIA): New define.
	(aarch64_linux_pauthregset): New variable declaration.