make more gimple_x_ptr accessors const correct

make more gimple_x_ptr accessors const correct

gcc/ChangeLog:

2015-10-05  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* gimple.h (gimple_op_ptr): Require a non const gimple *.
	(gimple_assign_lhs_ptr): Likewise.
	(gimple_assign_rhs1_ptr): Likewise.
	(gimple_assign_rhs2_ptr): Likewise.
	(gimple_assign_rhs3_ptr): Likewise.
	(gimple_call_lhs_ptr): Likewise.
	(gimple_call_fn_ptr): Likewise.
	(gimple_call_chain_ptr): Likewise.
		(gimple_call_arg_ptr): Likewise.
		(gimple_cond_lhs_ptr): Likewise.
	(gimple_cond_rhs_ptr): Likewise.
	(gimple_switch_index_ptr): Likewise.
	(gimple_return_retval_ptr): Likewise.

From-SVN: r228487