aarch64: Use memcpy to copy vector tables in vst2[q] intrinsics

aarch64: Use memcpy to copy vector tables in vst2[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 vst2[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 vst2q intrinsics.

gcc/ChangeLog:

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

	* config/aarch64/arm_neon.h (vst2_s64): Use __builtin_memcpy
	instead of constructing __builtin_aarch64_simd_oi one vector
	at a time.
	(vst2_u64): Likewise.
	(vst2_f64): Likewise.
	(vst2_s8): Likewise.
	(vst2_p8): Likewise.
	(vst2_s16): Likewise.
	(vst2_p16): Likewise.
	(vst2_s32): Likewise.
	(vst2_u8): Likewise.
	(vst2_u16): Likewise.
	(vst2_u32): Likewise.
	(vst2_f16): Likewise.
	(vst2_f32): Likewise.
	(vst2_p64): Likewise.
	(vst2q_s8): Likewise.
	(vst2q_p8): Likewise.
	(vst2q_s16): Likewise.
	(vst2q_p16): Likewise.
	(vst2q_s32): Likewise.
	(vst2q_s64): Likewise.
	(vst2q_u8): Likewise.
	(vst2q_u16): Likewise.
	(vst2q_u32): Likewise.
	(vst2q_u64): Likewise.
	(vst2q_f16): Likewise.
	(vst2q_f32): Likewise.
	(vst2q_f64): Likewise.
	(vst2q_p64): Likewise.

gcc/testsuite/ChangeLog:

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