RFR(S): 8214854: JDWP: Unforseen output truncation in logging

[Dmitry Chuyko]

Hello,

Please review a small fix for GCC 8.x warning in log_messages.c. Buffer 
sizes for parts of timestamp string can be adjusted to not exceed 
maximum buffer size when combined, while being able to hold necessary 
information.

webrev: http://cr.openjdk.java.net/~dchuyko/8214854/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8214854
testing: after the fix GCC 8 compiles working OpenJDK on Linux. 
Dev-submit job started.

-Dmitry