Avoid unnecessary ppeers_lock acquisition in exit1.

MFC after:	1 week
- Refactor defining variables.
- Merge common modules both i386 and amd64 into one if-endif.
- Sort.
- There are no functional changes.
1) For %Z format, understand "UTC" name too.
2) Return NULL if timegm() fails, because it means we can convert
what we have in GMT to local time needed.