aarch64: Add arm_streaming(_compatible) attributes

aarch64: Add arm_streaming(_compatible) attributes

This patch adds support for recognising the SME arm::streaming
and arm::streaming_compatible attributes.  These attributes
respectively describe whether the processor is definitely in
"streaming mode" (PSTATE.SM==1), whether the processor is
definitely not in streaming mode (PSTATE.SM==0), or whether
we don't know at compile time either way.

As far as the compiler is concerned, this effectively creates three
ISA submodes: streaming mode enables things that are not available
in non-streaming mode, non-streaming mode enables things that not
available in streaming mode, and streaming-compatible mode has to stick
to the common subset.  This means that some instructions are conditional
on PSTATE.SM==1 and some are conditional on PSTATE.SM==0.

I wondered about recording the streaming state in a new variable.
However, the set of available instructions is also influenced by
PSTATE.ZA (added later), so I think it makes sense to view this
as an instance of a more general mechanism.  Also, keeping the
PSTATE.SM state in the same flag variable as the other ISA
features makes it possible to sum up the requirements of an
ACLE function in a single value.

The patch therefore adds a new set of feature flags called "ISA modes".
Unlike the other two sets of flags (optional features and architecture-
level features), these ISA modes are not controlled directly by
command-line parameters or "target" attributes.

arm::streaming and arm::streaming_compatible are function type attributes
rather than function declaration attributes.  This means that we need
to find somewhere to copy the type information across to a function's
target options.  The patch does this in aarch64_set_current_function.

We also need to record which ISA mode a callee expects/requires
to be active on entry.  (The same mode is then active on return.)
The patch extends the current UNSPEC_CALLEE_ABI cookie to include
this information, as well as the PCS variant that it recorded
previously.

The attributes can also be written __arm_streaming and
__arm_streaming_compatible.  This has two advantages: it triggers
an error on compilers that don't understand the attributes, and it
eases use on C, where [[...]] attributes were only added in C23.

gcc/
	* config/aarch64/aarch64-isa-modes.def: New file.
	* config/aarch64/aarch64.h: Include it in the feature enumerations.
	(AARCH64_FL_SM_STATE, AARCH64_FL_ISA_MODES): New constants.
	(AARCH64_FL_DEFAULT_ISA_MODE): Likewise.
	(AARCH64_ISA_MODE): New macro.
	(CUMULATIVE_ARGS): Add an isa_mode field.
	* config/aarch64/aarch64-protos.h (aarch64_gen_callee_cookie): Declare.
	(aarch64_tlsdesc_abi_id): Return an arm_pcs.
	* config/aarch64/aarch64.cc (attr_streaming_exclusions)
	(aarch64_gnu_attributes, aarch64_gnu_attribute_table)
	(aarch64_arm_attributes, aarch64_arm_attribute_table): New tables.
	(aarch64_attribute_table): Redefine to include the gnu and arm
	attributes.
	(aarch64_fntype_pstate_sm, aarch64_fntype_isa_mode): New functions.
	(aarch64_fndecl_pstate_sm, aarch64_fndecl_isa_mode): Likewise.
	(aarch64_gen_callee_cookie, aarch64_callee_abi): Likewise.
	(aarch64_insn_callee_cookie, aarch64_insn_callee_abi): Use them.
	(aarch64_function_arg, aarch64_output_mi_thunk): Likewise.
	(aarch64_init_cumulative_args): Initialize the isa_mode field.
	(aarch64_output_mi_thunk): Use aarch64_gen_callee_cookie to get
	the ABI cookie.
	(aarch64_override_options): Add the ISA mode to the feature set.
	(aarch64_temporary_target::copy_from_fndecl): Likewise.
	(aarch64_fndecl_options, aarch64_handle_attr_arch): Likewise.
	(aarch64_set_current_function): Maintain the correct ISA mode.
	(aarch64_tlsdesc_abi_id): Return an arm_pcs.
	(aarch64_comp_type_attributes): Handle arm::streaming and
	arm::streaming_compatible.
	* config/aarch64/aarch64-c.cc (aarch64_define_unconditional_macros):
	Define __arm_streaming and __arm_streaming_compatible.
	* config/aarch64/aarch64.md (tlsdesc_small_<mode>): Use
	aarch64_gen_callee_cookie to get the ABI cookie.
	* config/aarch64/t-aarch64 (TM_H): Add all feature-related .def files.

gcc/testsuite/
	* gcc.target/aarch64/sme/aarch64-sme.exp: New harness.
	* gcc.target/aarch64/sme/streaming_mode_1.c: New test.
	* gcc.target/aarch64/sme/streaming_mode_2.c: Likewise.
	* gcc.target/aarch64/sme/keyword_macros_1.c: Likewise.
	* g++.target/aarch64/sme/aarch64-sme.exp: New harness.
	* g++.target/aarch64/sme/streaming_mode_1.C: New test.
	* g++.target/aarch64/sme/streaming_mode_2.C: Likewise.
	* g++.target/aarch64/sme/keyword_macros_1.C: Likewise.
	* gcc.target/aarch64/auto-init-1.c: Only expect the call insn
	to contain 1 (const_int 0), not 2.