Fix incorrect OpenBSD macro tests (fix testsuite failure)

The testsuite has been failing on OpenBSD, but an upcoming PR will fix this.

It was previously decided (ticket legacy/trac#20980 (moved)) that the OpenBSD macro would be used to test for OpenBSD (rather than __OpenBSD__, etc.) because the former seems to be defined on OpenBSD forks when the latter may or may not be.

However, sys/param.h needs to be included for this macro to be defined. There were many files where OpenBSD was tested for, but when sys/param.h was not included.

An upcoming PR will contain a fix to include sys/param.h in the files where the OpenBSD macro is used (when it is not included already). It will also change a couple of instances of the __OpenBSD__ macro to OpenBSD.

See commit 27df23ab where the usage of __OpenBSD__ and OPENBSD macros were replaced with OpenBSD.

See also tickets legacy/trac#6982 (moved) and legacy/trac#20980 (moved) where the various macros were discussed. The latter ticket is where it was decided to use the OpenBSD macro.

I tested on this box:

$ uname -mrs
OpenBSD 6.4 amd64

Before:

=============================================
   tor 0.4.0.0-alpha-dev: ./test-suite.log
=============================================

# TOTAL: 20
# PASS:  15
# SKIP:  4
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0

<snip>

options/validate__transproxy: [forking]
  FAIL src/test/test_options.c:1164: assert(tdata)
  [validate__transproxy FAILED]

<snip>

...and after:

=============================================
   tor 0.4.0.0-alpha-dev: ./test-suite.log
=============================================

# TOTAL: 20
# PASS:  16
# SKIP:  4
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0

Trac:
Username: kjak