Introduce gimple_transaction

Introduce gimple_transaction

This corresponds to:
  [PATCH 24/89] Introduce gimple_transaction
  https://gcc.gnu.org/ml/gcc-patches/2014-04/msg01207.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_transaction): New typedef.
	(const_gimple_transaction): New typedef.

	* gimple.h (gimple_build_transaction): Return a gimple_transaction
	rather than a plain gimple.
	(gimple_transaction_body_ptr): Require a gimple_transaction rather
	than a plain gimple.
	(gimple_transaction_body): Likewise.
	(gimple_transaction_label_ptr): Likewise.
	(gimple_transaction_set_body): Likewise.
	(gimple_transaction_set_label): Likewise.
	(gimple_transaction_set_subcode): Likewise.
	(gimple_transaction_label): Require a const_gimple_transaction
	rather than a plain const_gimple.
	(gimple_transaction_subcode): Likewise.

	* gimple-low.c (lower_stmt): Add checked cast to
	gimple_transaction within GIMPLE_TRANSACTION case of switch
	statement.

	* gimple-pretty-print.c (dump_gimple_transaction): Require a
	gimple_transaction rather than a plain gimple.
	(pp_gimple_stmt_1): Add checked cast to gimple_transaction within
	GIMPLE_TRANSACTION case of switch statement.
	* gimple-streamer-in.c (input_gimple_stmt): Likewise.
	* gimple-streamer-out.c (output_gimple_stmt): Likewise.
	* gimple-walk.c (walk_gimple_op): Likewise.
	(walk_gimple_stmt): Likewise.

	* gimple.c (gimple_build_transaction): Return a gimple_transaction
	rather than a plain gimple.
	(gimple_copy): Add checked casts to gimple_transaction within
	GIMPLE_TRANSACTION case of switch statement.

	* gimplify.c (gimplify_transaction): Split local "g" into
	"body_stmt" and "trans_stmt", strengthening the type of the latter
	from gimple to gimple_transaction.

	* omp-low.c (lower_omp_1): Add checked cast to gimple_transaction
	within GIMPLE_TRANSACTION case of switch statement.

	* trans-mem.c (diagnose_tm_1): Add checked cast within
	GIMPLE_TRANSACTION case of switch statement, introducing a new
	local "trans_stmt".  Use it in place of "stmt".
	(examine_call_tm): Convert local from gimple to gimple_transaction.
	(tm_region::get_transaction_stmt): New method.
	(tm_region::transaction_stmt): Add clarification of type to the
	comment.
	(tm_region_init_0): Require a gimple_transaction rather than a
	plain gimple.
	(tm_region_init): Convert a check against GIMPLE_TRANSACTION to a
	dyn_cast<gimple_transaction> and new local.
	(transaction_subcode_ior): Add a new local, using the new
	get_transaction_stmt method to perform a checked cast.
	(propagate_tm_flags_out): Likewise.
	(expand_transaction): Add a checked cast using the new
	get_transaction_stmt method.
	(generate_tm_state): Likewise.
	(execute_tm_mark): Likewise.
	(ipa_tm_diagnose_transaction): Likewise.

	* tree-cfg.c (verify_gimple_transaction): Require a
	gimple_transaction rather than a plain gimple.
	(make_edges): Add checked cast within GIMPLE_TRANSACTION case of
	switch statement
	(cleanup_dead_labels): Likewise.
	(verify_gimple_stmt): Likewise.
	(verify_gimple_in_seq_2): Likewise.
	(verify_gimple_in_seq_2): Likewise.
	(gimple_redirect_edge_and_branch): Add checked cast.

	* tree-inline.c (remap_gimple_stmt): Add checked cast within
	GIMPLE_TRANSACTION case of switch statement, introducing a new
	local "old_trans_stmt".  Use it in place of "stmt".  Add new
	local "new_trans_stmt", using it to initialize "copy", and for
	type-safe operations as a transaction.
	(estimate_num_insns): Add checked cast within GIMPLE_TRANSACTION
	case of switch statement.