aarch64: Move Neon vector-tuple type declaration into the compiler

aarch64: Move Neon vector-tuple type declaration into the compiler

Declare the Neon vector-tuple types inside the compiler instead of in
the arm_neon.h header. This is a necessary first step before adding
corresponding machine modes to the AArch64 backend.

The vector-tuple types are implemented using a #pragma. This means
initialization of builtin functions that have vector-tuple types as
arguments or return values has to be delayed until the #pragma is
handled.

gcc/ChangeLog:

2021-09-10  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-builtins.c (aarch64_init_simd_builtins):
	Factor out main loop to...
	(aarch64_init_simd_builtin_functions): This new function.
	(register_tuple_type): Define.
	(aarch64_scalar_builtin_type_p): Define.
	(handle_arm_neon_h): Define.
	* config/aarch64/aarch64-c.c (aarch64_pragma_aarch64): Handle
	pragma for arm_neon.h.
	* config/aarch64/aarch64-protos.h (aarch64_advsimd_struct_mode_p):
	Declare.
	(handle_arm_neon_h): Likewise.
	* config/aarch64/aarch64.c (aarch64_advsimd_struct_mode_p):
	Remove static modifier.
	* config/aarch64/arm_neon.h (target): Remove Neon vector
	structure type definitions.