re PR c++/41109 (Argument flagged as unused despite use in sizeof())

re PR c++/41109 (Argument flagged as unused despite use in sizeof())

	PR c++/41109
	PR c++/41110
	PR c++/41134
	* cp-tree.h (DECL_ODR_USED): New macro.
	(struct lang_decl_base): Add odr_used flag.
	* decl.c (duplicate_decls): Propagate it.  Use it for error.
	* pt.c (register_specialization): Use it for error.
	* decl2.c (mark_used): Use it as gating flag rather than TREE_USED.
	(cp_write_global_declarations): Use it for error.
	(tree_used_ok): Remove.
	* cp-tree.h: Remove tree_used_ok.
	* call.c (build_call_a): Don't call it.
	* init.c (build_offset_ref): Likewise.

From-SVN: r151061