[Bug c++/126840] New: ICE on invalid alignas() declaration with empty attribute argument

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126840

            Bug ID: 126840
           Summary: ICE on invalid alignas() declaration with empty
                    attribute argument
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: s.kimura.h41104 at gmail dot com
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/WhT65o86v

Reproducer:
```
int foo() {
  alignas() {}
  return 0;
}
```

Backtrace:
<source>:2:11: error: expected primary-expression before ')' token
    2 |   alignas() {}
      |           ^
<source>:3:10: internal compiler error: tree check: expected tree_list, have
error_mark in get_attribute_name, at attribs.cc:1062
    3 |   return 0;
      |          ^
0x2bae358 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x2ba2f9b internal_error(char const*, ...)
        ???:0
0xa3bc74 tree_check_failed(tree_node const*, char const*, int, char const*,
...)
        ???:0
0xd98493 c_parse_file()
        ???:0
0xf2b969 c_common_parse_file()
        ???:0


This ICE goes back to gcc-15:
https://godbolt.org/z/nEKnx5TPc