[AArch64] Add basic FP16 support

[AArch64] Add basic FP16 support

gcc/:

	* config/aarch64/aarch64-builtins.c (aarch64_fp16_type_node): New.
	(aarch64_init_builtins): Make aarch64_fp16_type_node, use for __fp16.

	* config/aarch64/aarch64-modes.def: Add HFmode.

	* config/aarch64/aarch64.h (TARGET_CPU_CPP_BUILTINS): Define
	__ARM_FP16_FORMAT_IEEE and __ARM_FP16_ARGS. Set bit 1 of __ARM_FP.

	* config/aarch64/aarch64.c (aarch64_init_libfuncs,
	aarch64_promoted_type): New.

	(aarch64_float_const_representable_p): Disable HFmode.
	(aarch64_mangle_type): Mangle half-precision floats to "Dh".
	(TARGET_PROMOTED_TYPE): Define to aarch64_promoted_type.
	(TARGET_INIT_LIBFUNCS): Define to aarch64_init_libfuncs.

	* config/aarch64/aarch64.md (mov<mode>): Include HFmode using GPF_F16.
	(movhf_aarch64, extendhfsf2, extendhfdf2, truncsfhf2, truncdfhf2): New.

	* config/aarch64/iterators.md (GPF_F16): New.

gcc/testsuite/:

	* gcc.target/aarch64/f16_movs_1.c: New test.

From-SVN: r226346