Make "maint info breakpoints" show "catch catch/throw/rethrow" locations

This commit makes "maint info breakpoints" show the internal locations
of C++ exception catchpoints:

 (gdb) info breakpoints
 Num     Type           Disp Enb Address            What
 2       catchpoint     keep y                      exception catch

With multiple locations:

 (gdb) maint info breakpoints
 Num     Type           Disp Enb Address            What
 2       catchpoint     keep y                      exception catch
 2.1                         y   0x000000000040545f <__cxa_begin_catch+95> inf 1
 2.2                         y   0x00007ffff71dbe0f <__cxxabiv1::__cxa_begin_catch(void*)+95> inf 1
 (gdb)

With a single location:

 (gdb) maint info breakpoints 2
 Num     Type           Disp Enb Address            What
 2       catchpoint     keep y                      exception catch inf 1
 2.1                         y   0x00007ffff7bc0b7f <__cxa_begin_catch+95> inf 1

With no locations:

 (gdb) maint info breakpoints 2
 Num     Type           Disp Enb Address            What
 2       catchpoint     keep y                      exception catch inf 1


Other catchpoints still show the same way, here a catch signal:

 (gdb) info breakpoints
 Num     Type           Disp Enb Address            What
 3       catchpoint     keep y                      signal "<standard signals>"

 (gdb) maint info breakpoints
 Num     Type           Disp Enb Address            What
 3       catchpoint     keep y                      signal "<standard signals>"  inf 1
 (gdb)

Note: I considered making the locations be printed from within
breakpoint_ops::print_one(), but gave up given the handling for the
broken MI v2 output:

 /* The mi2 broken format: the main breakpoint tuple ends here, the locations
     are outside.  */
  if (!use_fixed_output)
    bkpt_tuple_emitter.reset ();

in print_one_breakpoint.

gdb/ChangeLog:
2019-07-09  Pedro Alves  <palves@redhat.com>

	* break-catch-throw.c (is_exception_catchpoint): New.
	* breakpoint.c (print_one_breakpoint_location): New parameter
	'raw_loc'.  Handle it.  Use
	is_watchpoint/is_catchpoint/is_exception_catchpoint instead of
	looking at the breakpoint's type.
	(print_one_breakpoint): If handling "maint info breakpoints", also
	print locations of exception catchpoints.
	* breakpoint.h (is_exception_catchpoint): Declare.

gdb/break-catch-throw.c

@@ -83,6 +83,14 @@ struct exception_catchpoint : public breakpoint
   std::unique_ptr<compiled_regex> pattern;
 };
 
+/* See breakpoint.h.  */
+
+bool
+is_exception_catchpoint (breakpoint *bp)
+{
+  return bp->ops == &gnu_v3_exception_catchpoint_ops;
+}
+
 
 
 /* A helper function that fetches exception probe arguments.  This