[8u] RFR: 8250636: iso8601_time returns incorrect offset part on MacOS

[Sergey Nazarkin]

Original Bug: https://bugs.openjdk.java.net/browse/JDK-8250636
Review: https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2020-July/040894.html

Please review the backport of the fix for quite specific bug. The fix may be considered as ’too risky to fix’ since changes behavior existed for years.  

It appears Java for BSD-like systems (OSX particularly) prints time in iso8601format (used at GC logs) incorrectly.  Example of confused logs:

Europe/Moscow (DST isn't in use)
2020-07-30T11:29:10.350+0300 # Linux 
2020-07-30T11:29:10.350+0300 # Windows 
2020-07-30T11:29:10.350-0300 # MacOS 
Europe/Berlin (DST is in use)
2020-07-30T10:29:10.350+0200 # Linux 
2020-07-30T10:29:10.350+0200 # Windows 
2020-07-30T10:29:10.350-0100 # MacOS

The patch is not applied cleanly due to missed context and function signature change.

Webrev: http://cr.openjdk.java.net/~snazarki/jdk8u-dev-webrev/8250636/

Unfortunately the change breaks AIX build and additional patch need to be applied: 
https://bugs.openjdk.java.net/browse/JDK-8251365

Will create new review if this backport is considered as accepted. 

/Sergey