[Patch AArch64 13/17] Enable _Float16 for AArch64

[Patch AArch64 13/17] Enable _Float16 for AArch64

gcc/

	* config/aarch64/aarch64-c.c (aarch64_update_cpp_builtins): Update
	__FLT_EVAL_METHOD__ and __FLT_EVAL_METHOD_C99__ when we switch
	architecture levels.
	* config/aarch64/aarch64.c (aarch64_promoted_type): Only promote
	the aarch64_fp16_type_node, not all HFmode types.
	(aarch64_libgcc_floating_mode_supported_p): Support HFmode.
	(aarch64_scalar_mode_supported_p): Likewise.
	(aarch64_excess_precision): New.
	(TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P): Define.
	(TARGET_SCALAR_MODE_SUPPORTED_P): Likewise.
	(TARGET_C_EXCESS_PRECISION): Likewise.

gcc/testsuite/

	* gcc.target/aarch64/_Float16_1.c: New.
	* gcc.target/aarch64/_Float16_2.c: Likewise.
	* gcc.target/aarch64/_Float16_3.c: Likewise.

From-SVN: r242845