MFH: r429442

Improve the way CFLAGS and CPPFLAGS are set.

":?" is not supported by fmake from FreeBSD 9, so replace it with an explicit
version check. The end result was still the desired one (-DHAVE_STRCHRNUL=1 was
not passed on FreeBSD 9).

While here, also improve the version check by including DragonFly (which
supports strchrnul(3) according to its online man page) and restricting the
FreeBSD version check to the revision range after strchrnul(3) was added to
base.

Also stop passing -Os when building in debug mode, and set UNICODE61_CPPFLAGS
to pet portlint.

PR:		214608
Submitted by:	Pavel Volkov <pavelivolkov@gmail.com> (maintainer)

Approved by:	ports-secteam (junovitch)