P0490R0 GB 20: decomposition declaration should commit to tuple interpretation early

P0490R0 GB 20: decomposition declaration should commit to tuple interpretation early

	P0490R0 GB 20: decomposition declaration should commit to tuple
	interpretation early
	* decl.c (get_tuple_size): Make static.  If inst is error_mark_node
	or non-complete type, return NULL_TREE, otherwise if
	lookup_qualified_name fails or doesn't fold into INTEGER_CST, return
	error_mark_node.
	(get_tuple_element_type, get_tuple_decomp_init): Make static.
	(cp_finish_decomp): Pass LOC to get_tuple_size.  If it returns
	error_mark_node, complain and fail.

	* g++.dg/cpp1z/decomp10.C (f1): Adjust expected diagnostics.

From-SVN: r243724