gold: aarch64 split stack support

This patch adds gold support for split-stack function calling non-split
function on aarch64.

gold/ChangeLog:

	* gold/aarch64.c (AArch64_insn_utilities::aarch64_movn_decode_imm):
	New function.
	(AArch64_insn_utilities::aarch64_movk_decode_imm): Likewise.
	(AArch64_insn_utilities::clz_hwi): Likewise.
	(AArch64_insn_utilities::aarch64_bitmask_imm): Likewise.
	(Target_aarch64::do_calls_non_split): Likewise.
	* gold/testsuite/Makefile.am [DEFAULT_TARGET_AARCH64] (check_SCRIPTS):
	add split_aarch64.sh.
	[DEFAULT_TARGET_AARCH64] (check_DATA): Add split_aarch64_{1,2,3,4,r)
	tests.
	[DEFAULT_TARGET_AARCH64] (SPLIT_DEFSYMS): New rule.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_1.o): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_2.o): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_3.o): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_4.o): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_r.o): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_n.o): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_1): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_2): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_2.stdout): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_3.stdout): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_4): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_4.stdout): Likewise.
	[DEFAULT_TARGET_AARCH64] (split_aarch64_r.stdout): Likewise.
	[DEFAULT_TARGET_AARCH64] (MOSTLYCLEANFILES): Likewise.
	* gold/testsuite/split_aarch64.sh: New file.
	* gold/testsuite/split_aarch64_1.s: Likewise.
	* gold/testsuite/split_aarch64_2.s: Likewise.
	* gold/testsuite/split_aarch64_3.s: Likewise.
	* gold/testsuite/split_aarch64_4.s: Likewise.
	* gold/testsuite/split_aarch64_n.s: Likewise.