Add method to query current recording method to target_ops.

Signed-off-by: Tim Wiederhake <tim.wiederhake@intel.com>

gdb/ChangeLog

	* record-btrace.c (record_btrace_record_method): New function.
	(init_record_btrace_ops): Initialize to_record_method.
	* record-full.c (record_full_record_method): New function.
	(init_record_full_ops, init_record_full_core_ops): Add
	record_full_record_method.
	* record.h (enum record_method): New enum.
	* target-debug.h (target_debug_print_enum_record_method: New define.
	* target-delegates.c: Regenerate.
	* target.c (target_record_method): New function.
	* target.h: Include record.h.
	(struct target_ops) <to_record_method>: New field.
	(target_record_method): New export.

Change-Id: I05daa70e4e08a19901e848c731bb7d60cd87cc5a