RFR: 7164841: Improvements to the GC log file rotation

[Kirk Pepperdine]

> Append vs clobber: with or without rotation, -Xloggc always clobbers the last log. That's why people want a time stamp or pid in the gc file name, IMHO.

My client just clobbered his log files yet... I'd still *not* want the time stamp because this can potentially accidentally fill production disks. Better that my client over wrote the logs than filled his production disk because he didn't realize the behaviour. And, many don't realize the behaviour, they just follow the admin manual.

> 
> Alternatively, give an option to append when -Xloggc is enabled, vs default overwrite.

Allowing an append will break all current analysis tooling.

Regards,
Kirk