aarch64: Use memcpy to copy vector tables in vst3[q] intrinsics

aarch64: Use memcpy to copy vector tables in vst3[q] intrinsics

Use __builtin_memcpy to copy vector structures instead of building
a new opaque structure one vector at a time in each of the vst3[q]
Neon intrinsics in arm_neon.h. This simplifies the header file and
also improves code generation - superfluous move instructions were
emitted for every register extraction/set in this additional
structure.

Add new code generation tests to verify that superfluous move
instructions are no longer generated for the vst3q intrinsics.

gcc/ChangeLog:

2021-07-21  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/arm_neon.h (vst3_s64): Use __builtin_memcpy
	instead of constructing __builtin_aarch64_simd_ci one vector
	at a time.
	(vst3_u64): Likewise.
	(vst3_f64): Likewise.
	(vst3_s8): Likewise.
	(vst3_p8): Likewise.
	(vst3_s16): Likewise.
	(vst3_p16): Likewise.
	(vst3_s32): Likewise.
	(vst3_u8): Likewise.
	(vst3_u16): Likewise.
	(vst3_u32): Likewise.
	(vst3_f16): Likewise.
	(vst3_f32): Likewise.
	(vst3_p64): Likewise.
	(vst3q_s8): Likewise.
	(vst3q_p8): Likewise.
	(vst3q_s16): Likewise.
	(vst3q_p16): Likewise.
	(vst3q_s32): Likewise.
	(vst3q_s64): Likewise.
	(vst3q_u8): Likewise.
	(vst3q_u16): Likewise.
	(vst3q_u32): Likewise.
	(vst3q_u64): Likewise.
	(vst3q_f16): Likewise.
	(vst3q_f32): Likewise.
	(vst3q_f64): Likewise.
	(vst3q_p64): Likewise.

gcc/testsuite/ChangeLog:

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