[PATCH 2/3][GCC][AARCH64] Add new -mbranch-protection option to combine pointer signing and BTI

gcc/ChangeLog:

2019-01-08  Sam Tebbs  <sam.tebbs@arm.com>

	* config/aarch64/aarch64.c (BRANCH_PROTECT_STR_MAX,
	aarch64_parse_branch_protection,
	struct aarch64_branch_protect_type,
	aarch64_handle_no_branch_protection,
	aarch64_handle_standard_branch_protection,
	aarch64_validate_mbranch_protection,
	aarch64_handle_pac_ret_protection,
	aarch64_handle_attr_branch_protection,
	accepted_branch_protection_string,
	aarch64_pac_ret_subtypes,
	aarch64_branch_protect_types,
	aarch64_handle_pac_ret_leaf): Define.
	(aarch64_override_options_after_change_1, aarch64_override_options):
	Add check for accepted_branch_protection_string.
	(aarch64_option_save): Save accepted_branch_protection_string.
	(aarch64_option_restore): Save accepted_branch_protection_string.
	* config/aarch64/aarch64.c (aarch64_attributes): Add branch-protection.
	* config/aarch64/aarch64.opt: Add mbranch-protection. Deprecate
	msign-return-address.
	* doc/invoke.texi: Add mbranch-protection.

gcc/testsuite/Changelog:

2019-01-08  Sam Tebbs  <sam.tebbs@arm.com>

	* gcc.target/aarch64/(return_address_sign_1.c,
	return_address_sign_2.c, return_address_sign_3.c (__attribute__)):
	Change option to -mbranch-protection.
	* gcc.target/aarch64/(branch-protection-option.c,
	branch-protection-option-2.c, branch-protection-attr.c,
	branch-protection-attr-2.c): New file.

From-SVN: r267717