aarch64: Fix -fpack-struct + <arm_neon.h> [PR103147]

aarch64: Fix -fpack-struct + <arm_neon.h> [PR103147]

This PR is about -fpack-struct causing a crash when <arm_neon.h>
is included.  The new register_tuple_type code was expecting a
normal unpacked structure layout instead of a packed one.

For SVE we got around this by temporarily suppressing -fpack-struct,
so that the tuple types always have their normal ABI.  However:

(a) The SVE ACLE tuple types are defined to be abstract.  The fact
    that GCC uses structures is an internal implementation detail.

(b) In contrast, the ACLE explicitly defines the Advanced SIMD
    tuple types to be particular structures.

(c) Clang and previous versions of GCC are consistent in applying
    -fpack-struct to these tuple structures.

This patch therefore honours -fpack-struct and -fpack-struct=.  It also
adds tests for some other combinations, such as -mgeneral-regs-only and
-fpack-struct -mstrict-align.

gcc/
	PR target/103147
	* config/aarch64/aarch64-protos.h (aarch64_simd_switcher): New class.
	* config/aarch64/aarch64-sve-builtins.h (sve_switcher): Inherit
	from aarch64_simd_switcher.
	* config/aarch64/aarch64-builtins.cc (aarch64_simd_tuple_modes):
	New variable.
	(aarch64_lookup_simd_builtin_type): Use it instead of TYPE_MODE.
	(register_tuple_type): Add more asserts.  Expect the alignment
	of the structure to be subject to flag_pack_struct and
	maximum_field_alignment.  Set aarch64_simd_tuple_modes.
	(aarch64_simd_switcher::aarch64_simd_switcher): New function.
	(aarch64_simd_switcher::~aarch64_simd_switcher): Likewise.
	(handle_arm_neon_h): Hold an aarch64_simd_switcher throughout.
	(aarch64_general_init_builtins): Hold an aarch64_simd_switcher
	while calling aarch64_init_simd_builtins.
	* config/aarch64/aarch64-sve-builtins.cc (sve_switcher::sve_switcher)
	(sve_switcher::~sve_switcher): Remove code now performed by
	aarch64_simd_switcher.

gcc/testsuite/
	PR target/103147
	* gcc.target/aarch64/pr103147-1.c: New test.
	* gcc.target/aarch64/pr103147-2.c: Likewise.
	* gcc.target/aarch64/pr103147-3.c: Likewise.
	* gcc.target/aarch64/pr103147-4.c: Likewise.
	* gcc.target/aarch64/pr103147-5.c: Likewise.
	* gcc.target/aarch64/pr103147-6.c: Likewise.
	* gcc.target/aarch64/pr103147-7.c: Likewise.
	* gcc.target/aarch64/pr103147-8.c: Likewise.
	* gcc.target/aarch64/pr103147-9.c: Likewise.
	* gcc.target/aarch64/pr103147-10.c: Likewise.
	* g++.target/aarch64/pr103147-1.C: Likewise.
	* g++.target/aarch64/pr103147-2.C: Likewise.
	* g++.target/aarch64/pr103147-3.C: Likewise.
	* g++.target/aarch64/pr103147-4.C: Likewise.
	* g++.target/aarch64/pr103147-5.C: Likewise.
	* g++.target/aarch64/pr103147-6.C: Likewise.
	* g++.target/aarch64/pr103147-7.C: Likewise.
	* g++.target/aarch64/pr103147-8.C: Likewise.
	* g++.target/aarch64/pr103147-9.C: Likewise.
	* g++.target/aarch64/pr103147-10.C: Likewise.