rtos: free gdb packet allocated memory

compile tested only.

Change-Id: I3bc06c212967a3ce44a875f802b554c178537d1d
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/2382
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

src/rtos/linux.c

@@ -1149,6 +1149,7 @@ int linux_gdb_thread_packet(struct target *target,
 	}
 
 	gdb_put_packet(connection, out_str, strlen(out_str));
+	free(out_str);
 	return ERROR_OK;
 }