[GDB] Obey flow control when GDB connects.

src/core/gdbstub.c

 		stub->parse = gdbstub_state_new;
 	} else if ( ch == '-' ) {
 		gdbstub_tx_packet ( stub ); /* retransmit */
+	} else if ( ch == '$' ) {
+		/* GDB is reconnecting, drop our packet and listen to GDB */
+		stub->trans->send ( "-", 1 );
+		stub->parse = gdbstub_state_new;
 	}
 }