libcc1: add more uses of 'deleter'

This changes libcc1 to use the 'deleter' template in a few more
places.  The template and basic specializations are moved to a new
header, then some unmarshall functions are changed to use this code.
This change avoids the need to repeat cleanup code in the
unmarshallers.

libcc1

	* rpc.hh (deleter): Move template and some specializations to
	deleter.hh.
	(argument_wrapper<const T *>): Use cc1_plugin::unique_ptr.
	* marshall.cc (cc1_plugin::unmarshall): Use
	cc1_plugin::unique_ptr.
	* marshall-cp.hh (deleter): New specializations.
	(unmarshall): Use cc1_plugin::unique_ptr.
	* deleter.hh: New file.