Introduce gimple_resx

Introduce gimple_resx

This corresponds to:
  [PATCH 29/89] Introduce gimple_resx
  https://gcc.gnu.org/ml/gcc-patches/2014-04/msg01161.html
from the original 89-patch kit

That earlier patch was approved by Jeff:
> OK after fixing up the naming/const stuff as discussed for prior
> patches.
> That applies to 22-30. Make sure to take care of
> the pretty printers per Trevor's comments as well. He indicated those
> were missing in a couple of those patches.
in https://gcc.gnu.org/ml/gcc-patches/2014-05/msg00628.html

gcc/
	* coretypes.h (gimple_resx): New typedef.
	(const_gimple_resx): New typedef.

	* gimple.h (gimple_build_resx): Return a gimple_resx rather than a
	plain gimple.
	(gimple_resx_region): Require a const_gimple_resx rather than a
	plain const_gimple.
	(gimple_resx_set_region): Require a gimple_resx rather than a
	plain gimple.

	* gimple-pretty-print.c (dump_gimple_resx): Require a gimple_resx
	rather than a plain gimple.
	(pp_gimple_stmt_1): Add a checked cast to gimple_resx within
	GIMPLE_RESX case of switch statement.

	* gimple-streamer-in.c (input_gimple_stmt): Likewise.

	* gimple-streamer-out.c (output_gimple_stmt): Likewise.

	* gimple.c (gimple_build_resx): Return a gimple_resx rather than
	a plain gimple.

	* tree-cfg.c (move_stmt_r): Add a checked cast to gimple_resx
	within GIMPLE_RESX case of switch statement, adding a new local.

	* tree-eh.c (emit_resx): Convert local "x" from gimple to
	gimple_resx.
	(lower_resx): Require a gimple_resx rather than a plain gimple.
	(pass_lower_resx::execute): Add a checked cast to gimple_resx.
	(mark_reachable_handlers): Likewise.

	* tree-inline.c (remap_gimple_stmt): Add a checked cast to
	gimple_resx within GIMPLE_RESX case of switch statement, adding
	a new local.