c++: ICE with anonymous union [PR97974]

c++: ICE with anonymous union [PR97974]

While working on the GCC 11 patch, it occurred to me that we could move
the errors about invalid members from finish_struct_anon_r to here, so we
properly get a diagnostic in g++.law/union4.C.

gcc/cp/ChangeLog:

	PR c++/97974
	* class.c (finish_struct_anon_r): Drop complain parm.
	Remove non-field diagnostic.
	(finish_struct_anon): Adjust.
	* decl.c (fixup_anonymous_aggr): Move non-field diagnostic here.

gcc/testsuite/ChangeLog:

	PR c++/97974
	* g++.old-deja/g++.law/union4.C: Add expected diagnostic.