PR c++/86981, Implement -Wpessimizing-move.

PR c++/86981, Implement -Wpessimizing-move.

	* c.opt (Wpessimizing-move): New option.

	* typeck.c (decl_in_std_namespace_p): New.
	(is_std_move_p): New.
	(maybe_warn_pessimizing_move): New.
	(can_do_nrvo_p): New, factored out of ...
	(check_return_expr): ... here.  Warn about potentially harmful
	std::move in a return statement.

	* doc/invoke.texi: Document -Wpessimizing-move.

	* g++.dg/cpp0x/Wpessimizing-move1.C: New test.
	* g++.dg/cpp0x/Wpessimizing-move2.C: New test.
	* g++.dg/cpp0x/Wpessimizing-move3.C: New test.
	* g++.dg/cpp0x/Wpessimizing-move4.C: New test.
	* g++.dg/cpp1z/Wpessimizing-move1.C: New test.

From-SVN: r263741