Don't memset non-POD types: struct breakpoint

Don't memset non-POD types: struct breakpoint

Eh, struct breakpoint was made non-POD just today, with commit
d28cd78ad820e3 ("Change breakpoint event locations to
event_location_up").  :-)

  src/gdb/breakpoint.c: In function ‘void init_raw_breakpoint_without_location(breakpoint*, gdbarch*, bptype, const breakpoint_ops*)’:
  src/gdb/breakpoint.c:7447:28: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = breakpoint; <template-parameter-1-2> = void; size_t = long unsigned int]’
     memset (b, 0, sizeof (*b));
			      ^
  In file included from src/gdb/common/common-defs.h:85:0,
		   from src/gdb/defs.h:28,
		   from src/gdb/breakpoint.c:20:
  src/gdb/common/poison.h:56:7: note: declared here
   void *memset (T *s, int c, size_t n) = delete;
	 ^

gdb/ChangeLog:
2017-04-25  Pedro Alves  <palves@redhat.com>

	* breakpoint.h (struct breakpoint): In-class initialize all
	fields.  Make boolean fields "bool".
	* breakpoint.c (init_raw_breakpoint_without_location): Remove
	memset call and initializations no longer necessary.