Implement LWG2296 helper intrinsic
c-family/
	* c-common.h (enum rid): Add RID_ADDRESSOF.
	* c-common.c (c_common_reswords): Add __builtin_addressof.
cp/
	* parser.c (cp_parser_postfix_expression): Handle RID_ADDRESSOF.
	* cp-objcp-common.c (cp_common_init_ts): Handle ADDRESSOF_EXPR.
	* constexpr.c (potential_constant_expression_1): Likewise.
	* error.c (dump_expr): Likewise.
	* typeck.c (cp_build_addressof): New function.
	* cp-tree.h (cp_build_addressof): Declare.
	* cxx-pretty-print.h (pp_cxx_addressof_expression): Declare.
	* cp-tree.def (ADDRESSOF_EXPR): New tree code.
	* cxx-pretty-print.c (cxx_pretty_printer::primary_expression): Handle
	ADDRESSOF_EXPR.  Add __builtin_addressof and
	__has_unique_object_representations into syntax in function comment.
	(pp_cxx_addressof_expression): New function.
	* pt.c (tsubst_copy_and_build): Handle ADDRESSOF_EXPR.
testsuite/
	* g++.dg/cpp0x/addressof1.C: New test.
	* g++.dg/cpp0x/addressof2.C: New test.

From-SVN: r240873