PR c++/83205
	* decl.c (cp_finish_decomp): Handle the case when tsize is not
	error_mark_node, but doesn't fit into uhwi.  Split up count != eltscnt
	and !tree_fits_uhwi_p (tsize) error_at calls into error_n and inform_n
	to handle plural forms properly.

	* g++.dg/cpp1z/decomp3.C: Adjust for structured binding count
	mismatch diagnostics split into error and warning with plural
	forms.
	* g++.dg/cpp1z/decomp10.C: Likewise.
	* g++.dg/cpp1z/decomp32.C: New test.

From-SVN: r255706