gdb: give names to async event/signal handlers

gdb: give names to async event/signal handlers

Assign names to async event/signal handlers.  They will be used in debug
messages when file handlers are invoked.

Unlike in the previous patch, the names are not copied in the structure,
since we don't need to (all names are string literals for the moment).

gdb/ChangeLog:

	* async-event.h (create_async_signal_handler): Add name
	parameter.
	(create_async_event_handler): Likewise.
	* async-event.c (struct async_signal_handler) <name>: New field.
	(struct async_event_handler) <name>: New field.
	(create_async_signal_handler): Assign name.
	(create_async_event_handler): Assign name.
	* event-top.c (async_init_signals): Pass name when creating
	handler.
	* infrun.c (_initialize_infrun): Likewise.
	* record-btrace.c (record_btrace_push_target): Likewise.
	* record-full.c (record_full_open): Likewise.
	* remote-notif.c (remote_notif_state_allocate): Likewise.
	* remote.c (remote_target::open_1): Likewise.
	* tui/tui-win.c (tui_initialize_win): Likewise.

Change-Id: Icd9d9f775542ae5fc2cd148c12f481e7885936d5