Use ui_out_emit_tuple in tracepoint.c

Use ui_out_emit_tuple in tracepoint.c

This changes some code in tracepoint.c to use ui_out_emit_tuple.  One
of these involved removing an otherwise unrelated cleanup (changing
type to std::string) and the other involved introducing a new block.

ChangeLog
2017-04-22  Tom Tromey  <tom@tromey.com>

	* tracepoint.c (tvariables_info_1)
	(print_one_static_tracepoint_marker): Use ui_out_emit_tuple.