Make structs breakpoint/base_breakpoint/catchpoint be abstract

You should never instanciate these types directly.

Change-Id: I8086c74c415eadbd44924bb0ef20f34b5b97ee6f

gdb/breakpoint.c

@@ -252,6 +252,21 @@ static const struct breakpoint_ops tracepoint_probe_breakpoint_ops =
   create_breakpoints_sal,
 };
 
+/* Implementation of abstract dtors.  These must exist to satisfy the
+   linker.  */
+
+breakpoint::~breakpoint ()
+{
+}
+
+base_breakpoint::~base_breakpoint ()
+{
+}
+
+catchpoint::~catchpoint ()
+{
+}
+
 /* The structure to be used in regular breakpoints.  */
 struct ordinary_breakpoint : public base_breakpoint
 {

gdb/breakpoint.h

@@ -631,7 +631,7 @@ struct breakpoint
 
   DISABLE_COPY_AND_ASSIGN (breakpoint);
 
-  virtual ~breakpoint () = default;
+  virtual ~breakpoint () = 0;
 
   /* Allocate a location for this breakpoint.  */
   virtual struct bp_location *allocate_location ();
@@ -862,6 +862,8 @@ struct base_breakpoint : public breakpoint
 {
   using breakpoint::breakpoint;
 
+  ~base_breakpoint () override = 0;
+
   void re_set () override;
   int insert_location (struct bp_location *) override;
   int remove_location (struct bp_location *,
@@ -1023,6 +1025,8 @@ struct catchpoint : public base_breakpoint
      COND_STRING is not NULL, then store it in the breakpoint.  */
   catchpoint (struct gdbarch *gdbarch, bool temp, const char *cond_string);
 
+  ~catchpoint () override = 0;
+
   void re_set () override
   {
     /* For catchpoints, the default is to do nothing.  */