Older unix systems included a timezone function, which has nothing in common with linux timezone variable. The test to check whether timezone exists in configure.in is bogus. Moreover, the systematic addition of timezone in build/ParseChangelog.c is bogus as well.
Can you send a patch please? It's hard to guess what OpenBSD needs otherwise.
If you append a patch to this report, I will try to include.
Please reopen with a patch.