Since TRAIT_EXPR is exceptional, maybe_wrap_with_location won't wrap it, so
we need to put its location in the TRAIT_EXPR node itself.

	* cp-tree.h (TRAIT_EXPR_LOCATION): New.
	(struct tree_trait_expr): Add locus field.
	* parser.c (cp_parser_trait_expr): Pass trait_loc down.
	* pt.c (tsubst_copy_and_build) [TRAIT_EXPR]: Likewise.
	* semantics.c (finish_trait_expr): Add location parm.
	* tree.c (cp_expr_location): Handle TRAIT_EXPR.

From-SVN: r275260