Create sub classes of 'struct breakpoint'

Create sub classes of 'struct breakpoint'

Nowadays, there are three types of breakpoint in GDBserver,

 - gdb breakpoints,
 - reinsert breakpoints, used for software single step,
 - other breakpoints, used for tracepoint,

but we only have one 'struct breakpoint' for all of them.  Some fields
are only useful to one type of breakpoint.  For example, cond_list
and command_list are only used by gdb breakpoints, while handler is
only used by other breakpoints.

This patch changes 'struct breakpoint' to a base class, which has fields
needed by all breakpoint types, also add three sub-classes to
'struct breakpoint' to these three types of breakpoints.

gdb/gdbserver:

2016-07-21  Yao Qi  <yao.qi@linaro.org>

	* mem-break.c (struct breakpoint) <cond_list>: Remove.
	<command_list, handler>: Remove.
	(struct gdb_breakpoint): New.
	(struct other_breakpoint): New.
	(struct reinsert_breakpoint): New.
	(is_gdb_breakpoint): New function.
	(any_persistent_commands): Update command_list if
	is_gdb_breakpoint returns true.
	(set_breakpoint): Create breakpoints according to their types.
	(find_gdb_breakpoint): Return 'struct gdb_breakpoint *'.
	(set_gdb_breakpoint_1): Likewise.
	(set_gdb_breakpoint): Likewise.
	(clear_breakpoint_conditions): Change parameter type to
	'struct gdb_breakpoint *'.
	(clear_breakpoint_commands): Likewise.
	(clear_breakpoint_conditions_and_commands): Likewise.
	(add_condition_to_breakpoint): Likewise.
	(add_breakpoint_condition): Likewise.
	(add_commands_to_breakpoint): Likewise.
	(check_breakpoints): Check other_breakpoint.
	(clone_one_breakpoint): Clone breakpopint according to its type.
	* mem-break.h (struct gdb_breakpoint): Declare.
	(set_gdb_breakpoint): Update declaration.
	(clear_breakpoint_conditions_and_commands): Likewise.
	(add_breakpoint_condition): Likewise.
	(add_breakpoint_commands): Likewise.
	* server.c (process_point_options): Change parameter type to
	'struct gdb_breakpoint *'.