c++: Diagnose attributes on class/enum declarations [PR110345]

c++: Diagnose attributes on class/enum declarations [PR110345]

The following testcase shows another issue where we just ignored
attributes without telling user we did that.

If there are any declarators, the ignoring of the attribute
are diagnosed in grokdeclarator etc., but if there is none
(and we don't error such as on
int;
), the following patch emits diagnostics.

2024-12-18  Jakub Jelinek  <jakub@redhat.com>

	PR c++/110345
	* decl.cc (check_tag_decl): Diagnose std_attributes.

	* g++.dg/cpp0x/gen-attrs-86.C: New test.