The ARMv8.2-A FP16 extension adds to both the VFP and the NEON
instruction sets. This patch adds support to the testsuite to select
targets and set options for tests that make use of these
instructions. It also adds documentation for ARMv8.1-A selectors.

Tested the series for arm-none-linux-gnueabihf with native bootstrap and
make check and for arm-none-eabi and armeb-none-eabi with make check on an
ARMv8.2-A emulator.

Ok for trunk?
Matthew

2016-05-17  Matthew Wahab  <matthew.wahab@arm.com>

	* doc/sourcebuild.texi (ARM-specific attributes): Add entries for
         arm_v8_1a_neon_ok, arm_v8_2a_fp16_scalar_ok, arm_v8_2a_fp16_scalar_hw,
	arm_v8_2a_fp16_neon_ok and arm_v8_2a_fp16_neon_hw.
	(Add options): Add entries for arm_v8_1a_neon, arm_v8_2a_scalar,
	arm_v8_2a_neon.

testsuite/
2016-05-17  Matthew Wahab  <matthew.wahab@arm.com>

	* lib/target-supports.exp
	(add_options_for_arm_v8_2a_fp16_scalar_ok): New.
	(add_options_for_arm_v8_2a_fp16_neon): New.
	(check_effective_target_arm_arch_v8_2a_ok): Auto-generate.
	(add_options_for_arm_arch_v8_2a): Auto-generate.
	(check_effective_target_arm_arch_v8_2a_multilib): Auto-generate.
	(check_effective_target_arm_v8_2a_fp16_scalar_ok_nocache): New.
	(check_effective_target_arm_v8_2a_fp16_scalar_ok): New.
	(check_effective_target_arm_v8_2a_fp16_neon_ok_nocache): New.
	(check_effective_target_arm_v8_2a_fp16_neon_ok): New.
	(check_effective_target_arm_v8_2a_fp16_scalar_hw): New.
	(check_effective_target_arm_v8_2a_fp16_neon_hw): New.