aarch64: Use memcpy to copy structures in vst4[q]_lane intrinsics

aarch64: Use memcpy to copy structures in vst4[q]_lane intrinsics

Use __builtin_memcpy to copy vector structures instead of using a
union - or constructing a new opaque structure one vector at a time -
in each of the vst4[q]_lane Neon intrinsics in arm_neon.h.

Add new code generation tests to verify that superfluous move
instructions are not generated for the vst4q_lane intrinsics.

gcc/ChangeLog:

2021-07-29  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/arm_neon.h (__ST4_LANE_FUNC): Delete.
	(__ST4Q_LANE_FUNC): Delete.
	(vst4_lane_f16): Use __builtin_memcpy to copy vector
	structure instead of constructing __builtin_aarch64_simd_xi
	one vector at a time.
	(vst4_lane_f32): Likewise.
	(vst4_lane_f64): Likewise.
	(vst4_lane_p8): Likewise.
	(vst4_lane_p16): Likewise.
	(vst4_lane_p64): Likewise.
	(vst4_lane_s8): Likewise.
	(vst4_lane_s16): Likewise.
	(vst4_lane_s32): Likewise.
	(vst4_lane_s64): Likewise.
	(vst4_lane_u8): Likewise.
	(vst4_lane_u16): Likewise.
	(vst4_lane_u32): Likewise.
	(vst4_lane_u64): Likewise.
	(vst4_lane_bf16): Likewise.
	(vst4q_lane_f16): Use __builtin_memcpy to copy vector
	structure instead of using a union.
	(vst4q_lane_f32): Likewise.
	(vst4q_lane_f64): Likewise.
	(vst4q_lane_p8): Likewise.
	(vst4q_lane_p16): Likewise.
	(vst4q_lane_p64): Likewise.
	(vst4q_lane_s8): Likewise.
	(vst4q_lane_s16): Likewise.
	(vst4q_lane_s32): Likewise.
	(vst4q_lane_s64): Likewise.
	(vst4q_lane_u8): Likewise.
	(vst4q_lane_u16): Likewise.
	(vst4q_lane_u32): Likewise.
	(vst4q_lane_u64): Likewise.
	(vst4q_lane_bf16): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/vector_structure_intrinsics.c: Add new
	tests.