c++: Implement C++ DR 2262 - Attributes for asm-definition [PR110734]

c++: Implement C++ DR 2262 - Attributes for asm-definition [PR110734]

Seems in 2017 attribute-specifier-seq[opt] was added to asm-declaration
and the change was voted in as a DR.

The following patch implements it by parsing the attributes and warning
about them.

I found one attribute parsing bug I'll send a fix for momentarily.

And there is another thing I wonder about: with -Wno-attributes= we are
supposed to ignore the attributes altogether, but we are actually still
warning about them when we emit these generic warnings about ignoring
all attributes which appertain to this and that (perhaps with some
exceptions we first remove from the attribute chain), like:
void foo () { [[foo::bar]]; }
with -Wattributes -Wno-attributes=foo::bar
Shouldn't we call some helper function in cases like this and warn
not when std_attrs (or how the attribute chain var is called) is non-NULL,
but if it is non-NULL and contains at least one non-attribute_ignored_p
attribute?  cp_parser_declaration at least tries:
      if (std_attrs != NULL_TREE && !attribute_ignored_p (std_attrs))
        warning_at (make_location (attrs_loc, attrs_loc, parser->lexer),
                    OPT_Wattributes, "attribute ignored");
but attribute_ignored_p here checks the first attribute rather than the
whole chain.  So it will incorrectly not warn if there is an ignored
attribute followed by non-ignored.

2023-12-05  Jakub Jelinek  <jakub@redhat.com>

	PR c++/110734
	* parser.cc (cp_parser_block_declaration): Implement C++ DR 2262
	- Attributes for asm-definition.  Call cp_parser_asm_definition
	even if RID_ASM token is only seen after sequence of standard
	attributes.
	(cp_parser_asm_definition): Parse standard attributes before
	RID_ASM token and warn for them with -Wattributes.

	* g++.dg/DRs/dr2262.C: New test.
	* g++.dg/cpp0x/gen-attrs-76.C (foo, bar): Don't expect errors
	on attributes on asm definitions.
	* g++.dg/gomp/attrs-11.C: Remove 2 expected errors.