Allow target attributes in non-gnu namespaces

Currently there are four static sources of attributes:

- LANG_HOOKS_ATTRIBUTE_TABLE
- LANG_HOOKS_COMMON_ATTRIBUTE_TABLE
- LANG_HOOKS_FORMAT_ATTRIBUTE_TABLE
- TARGET_ATTRIBUTE_TABLE

All of the attributes in these tables go in the "gnu" namespace.
This means that they can use the traditional GNU __attribute__((...))
syntax and the standard [[gnu::...]] syntax.

Standard attributes are registered dynamically with a null namespace.
There are no supported attributes in other namespaces (clang, vendor
namespaces, etc.).

This patch tries to generalise things by making the namespace
part of the attribute specification.

It's usual for multiple attributes to be defined in the same namespace,
so rather than adding the namespace to each individual definition,
it seemed better to group attributes in the same namespace together.
This would also allow us to reuse the same table for clang attributes
that are written with the GNU syntax, or other similar situations
where the attribute can be accessed via multiple "spellings".

The patch therefore adds a scoped_attribute_specs that contains
a namespace and a list of attributes in that namespace.

It's still possible to have multiple scoped_attribute_specs
for the same namespace.  E.g. it makes sense to keep the
C++-specific, C/C++-common, and format-related attributes in
separate tables, even though they're all GNU attributes.

Current lists of attributes are terminated by a null name.
Rather than keep that for the new structure, it seemed neater
to use an array_slice.  This also makes the tables slighly more
compact.

In general, a target might want to support attributes in multiple
namespaces.  Rather than have a separate hook for each possibility
(like the three langhooks above), it seemed better to make
TARGET_ATTRIBUTE_TABLE a table of tables.  Specifically, it's
an array_slice of scoped_attribute_specs.

We can do the same thing for langhooks, which allows the three hooks
above to be merged into a single LANG_HOOKS_ATTRIBUTE_TABLE.
It also allows the standard attributes to be registered statically
and checked by the usual attribs.cc checks.

The patch adds a TARGET_GNU_ATTRIBUTES helper for the common case
in which a target wants a single table of gnu attributes.  It can
only be used if the table is free of preprocessor directives.

There are probably other things we need to do to make vendor namespaces
work smoothly.  E.g. in principle it would be good to make exclusion
sets namespace-aware.  But to some extent we have that with standard
vs. gnu attributes too.  This patch is just supposed to be a first step.

gcc/
	* attribs.h (scoped_attribute_specs): New structure.
	(register_scoped_attributes): Take a reference to a
	scoped_attribute_specs instead of separate namespace and array
	parameters.
	* plugin.h (register_scoped_attributes): Likewise.
	* attribs.cc (register_scoped_attributes): Likewise.
	(attribute_tables): Change into an array of scoped_attribute_specs
	pointers.  Reduce to 1 element for frontends and 1 element for targets.
	(empty_attribute_table): Delete.
	(check_attribute_tables): Update for changes to attribute_tables.
	Use a hash_set to identify duplicates.
	(handle_ignored_attributes_option): Update for above changes.
	(init_attributes): Likewise.
	(excl_pair): Delete.
	(test_attribute_exclusions): Update for above changes.  Don't
	enforce symmetry for standard attributes in the top-level namespace.
	* langhooks-def.h (LANG_HOOKS_COMMON_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_FORMAT_ATTRIBUTE_TABLE): Likewise.
	(LANG_HOOKS_INITIALIZER): Update accordingly.
	(LANG_HOOKS_ATTRIBUTE_TABLE): Define to an empty constructor.
	* langhooks.h (lang_hooks::common_attribute_table): Delete.
	(lang_hooks::format_attribute_table): Likewise.
	(lang_hooks::attribute_table): Redefine to an array of
	scoped_attribute_specs pointers.
	* target-def.h (TARGET_GNU_ATTRIBUTES): New macro.
	* target.def (attribute_spec): Redefine to return an array of
	scoped_attribute_specs pointers.
	* tree-inline.cc (function_attribute_inlinable_p): Update accordingly.
	* doc/tm.texi: Regenerate.
	* config/aarch64/aarch64.cc (aarch64_attribute_table): Define using
	TARGET_GNU_ATTRIBUTES.
	* config/alpha/alpha.cc (vms_attribute_table): Likewise.
	* config/avr/avr.cc (avr_attribute_table): Likewise.
	* config/bfin/bfin.cc (bfin_attribute_table): Likewise.
	* config/bpf/bpf.cc (bpf_attribute_table): Likewise.
	* config/csky/csky.cc (csky_attribute_table): Likewise.
	* config/epiphany/epiphany.cc (epiphany_attribute_table): Likewise.
	* config/gcn/gcn.cc (gcn_attribute_table): Likewise.
	* config/h8300/h8300.cc (h8300_attribute_table): Likewise.
	* config/loongarch/loongarch.cc (loongarch_attribute_table): Likewise.
	* config/m32c/m32c.cc (m32c_attribute_table): Likewise.
	* config/m32r/m32r.cc (m32r_attribute_table): Likewise.
	* config/m68k/m68k.cc (m68k_attribute_table): Likewise.
	* config/mcore/mcore.cc (mcore_attribute_table): Likewise.
	* config/microblaze/microblaze.cc (microblaze_attribute_table):
	Likewise.
	* config/mips/mips.cc (mips_attribute_table): Likewise.
	* config/msp430/msp430.cc (msp430_attribute_table): Likewise.
	* config/nds32/nds32.cc (nds32_attribute_table): Likewise.
	* config/nvptx/nvptx.cc (nvptx_attribute_table): Likewise.
	* config/riscv/riscv.cc (riscv_attribute_table): Likewise.
	* config/rl78/rl78.cc (rl78_attribute_table): Likewise.
	* config/rx/rx.cc (rx_attribute_table): Likewise.
	* config/s390/s390.cc (s390_attribute_table): Likewise.
	* config/sh/sh.cc (sh_attribute_table): Likewise.
	* config/sparc/sparc.cc (sparc_attribute_table): Likewise.
	* config/stormy16/stormy16.cc (xstormy16_attribute_table): Likewise.
	* config/v850/v850.cc (v850_attribute_table): Likewise.
	* config/visium/visium.cc (visium_attribute_table): Likewise.
	* config/arc/arc.cc (arc_attribute_table): Likewise.  Move further
	down file.
	* config/arm/arm.cc (arm_attribute_table): Update for above changes,
	using...
	(arm_gnu_attributes, arm_gnu_attribute_table): ...these new globals.
	* config/i386/i386-options.h (ix86_attribute_table): Delete.
	(ix86_gnu_attribute_table): Declare.
	* config/i386/i386-options.cc (ix86_attribute_table): Replace with...
	(ix86_gnu_attributes, ix86_gnu_attribute_table): ...these two globals.
	* config/i386/i386.cc (ix86_attribute_table): Define as an array of
	scoped_attribute_specs pointers.
	* config/ia64/ia64.cc (ia64_attribute_table): Update for above changes,
	using...
	(ia64_gnu_attributes, ia64_gnu_attribute_table): ...these new globals.
	* config/rs6000/rs6000.cc (rs6000_attribute_table): Update for above
	changes, using...
	(rs6000_gnu_attributes, rs6000_gnu_attribute_table): ...these new
	globals.

gcc/ada/
	* gcc-interface/gigi.h (gnat_internal_attribute_table): Change
	type to scoped_attribute_specs.
	* gcc-interface/utils.cc (gnat_internal_attribute_table): Likewise,
	using...
	(gnat_internal_attributes): ...this as the underlying array.
	* gcc-interface/misc.cc (gnat_attribute_table): New global.
	(LANG_HOOKS_ATTRIBUTE_TABLE): Use it.

gcc/c-family/
	* c-common.h (c_common_attribute_table): Replace with...
	(c_common_gnu_attribute_table): ...this.
	(c_common_format_attribute_table): Change type to
	scoped_attribute_specs.
	* c-attribs.cc (c_common_attribute_table): Replace with...
	(c_common_gnu_attributes, c_common_gnu_attribute_table): ...these
	new globals.
	(c_common_format_attribute_table): Change type to
	scoped_attribute_specs, using...
	(c_common_format_attributes): ...this as the underlying array.

gcc/c/
	* c-tree.h (std_attribute_table): Declare.
	* c-decl.cc (std_attribute_table): Change type to
	scoped_attribute_specs, using...
	(std_attributes): ...this as the underlying array.
	(c_init_decl_processing): Remove call to register_scoped_attributes.
	* c-objc-common.h (c_objc_attribute_table): New global.
	(LANG_HOOKS_ATTRIBUTE_TABLE): Use it.
	(LANG_HOOKS_COMMON_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_FORMAT_ATTRIBUTE_TABLE): Delete.

gcc/cp/
	* cp-tree.h (cxx_attribute_table): Delete.
	(cxx_gnu_attribute_table, std_attribute_table): Declare.
	* cp-objcp-common.h (LANG_HOOKS_COMMON_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_FORMAT_ATTRIBUTE_TABLE): Delete.
	(cp_objcp_attribute_table): New table.
	(LANG_HOOKS_ATTRIBUTE_TABLE): Redefine.
	* tree.cc (cxx_attribute_table): Replace with...
	(cxx_gnu_attributes, cxx_gnu_attribute_table): ...these globals.
	(std_attribute_table): Change type to scoped_attribute_specs, using...
	(std_attributes): ...this as the underlying array.
	(init_tree): Remove call to register_scoped_attributes.

gcc/d/
	* d-tree.h (d_langhook_attribute_table): Replace with...
	(d_langhook_gnu_attribute_table): ...this.
	(d_langhook_common_attribute_table): Change type to
	scoped_attribute_specs.
	* d-attribs.cc (d_langhook_common_attribute_table): Change type to
	scoped_attribute_specs, using...
	(d_langhook_common_attributes): ...this as the underlying array.
	(d_langhook_attribute_table): Replace with...
	(d_langhook_gnu_attributes, d_langhook_gnu_attribute_table): ...these
	new globals.
	(uda_attribute_p): Update accordingly, and update for new
	targetm.attribute_table type.
	* d-lang.cc (d_langhook_attribute_table): New global.
	(LANG_HOOKS_COMMON_ATTRIBUTE_TABLE): Delete.

gcc/fortran/
	* f95-lang.cc: Include attribs.h.
	(gfc_attribute_table): Change to an array of scoped_attribute_specs
	pointers, using...
	(gfc_gnu_attributes, gfc_gnu_attribute_table): ...these new globals.

gcc/jit/
	* dummy-frontend.cc (jit_format_attribute_table): Change type to
	scoped_attribute_specs, using...
	(jit_format_attributes): ...this as the underlying array.
	(jit_attribute_table): Change to an array of scoped_attribute_specs
	pointers, using...
	(jit_gnu_attributes, jit_gnu_attribute_table): ...these new globals
	for the original array.  Include the format attributes.
	(LANG_HOOKS_COMMON_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_FORMAT_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_ATTRIBUTE_TABLE): Define.

gcc/lto/
	* lto-lang.cc (lto_format_attribute_table): Change type to
	scoped_attribute_specs, using...
	(lto_format_attributes): ...this as the underlying array.
	(lto_attribute_table): Change to an array of scoped_attribute_specs
	pointers, using...
	(lto_gnu_attributes, lto_gnu_attribute_table): ...these new globals
	for the original array.  Include the format attributes.
	(LANG_HOOKS_COMMON_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_FORMAT_ATTRIBUTE_TABLE): Delete.
	(LANG_HOOKS_ATTRIBUTE_TABLE): Define.