Remove cleanups from btrace code

Remove cleanups from btrace code

This removes some cleanups from the btrace code by minorly C++-ifying
struct btrace_data.

gdb/ChangeLog
2018-06-08  Tom Tromey  <tom@tromey.com>

	* common/btrace-common.h (struct btrace_data): Add constructor,
	destructor, move assignment operator.
	<empty, clear, fini>: New methods.
	<format>: Initialize.
	(btrace_data_init, btrace_data_fini, btrace_data_clear)
	(btrace_data_empty): Don't declare.
	* common/btrace-common.c (btrace_data_init): Remove.
	(btrace_data::fini): Rename from btrace_data_fini.
	(btrace_data::empty): Rename from btrace_data_empty.
	(btrace_data::clear): Rename from btrace_data_clear.  Return
	bool.
	* btrace.h (make_cleanup_btrace_data): Don't declare.
	* btrace.c (btrace_add_pc, btrace_stitch_trace, btrace_clear)
	(parse_xml_btrace): Update.
	(do_btrace_data_cleanup, make_cleanup_btrace_data): Remove.
	(maint_btrace_clear_packet_history_cmd): Update.

gdb/gdbserver/ChangeLog
2018-06-08  Tom Tromey  <tom@tromey.com>

	* linux-low.c (linux_low_read_btrace): Update.