JDWP: Unforseen output truncation in logging

GCC 8 reports an error:

src/jdk.jdwp.agent/share/native/libjdwp/log_messages.c:75:24: error: '%.3d' directive output may be truncated writing between 3 and 11 bytes into a region of size between 0 and 80 [-Werror=format-truncation=]
                    "%s.%.3d %s", timestamp_prefix,
                        ^~~~
The call is:
    (void)snprintf(tbuf, ltbuf,
                   "%s.%.3d %s", timestamp_prefix,
                   (int)(millisecs), timestamp_postfix);

It can be fixed by making prefix and postfix reasonably short, like:

char timestamp_prefix[MAXLEN_TIMESTAMP / 2 - 4];
char timestamp_postfix[MAXLEN_TIMESTAMP / 2];