marking BSD-variant OSes

[David Holland <dholland-pkgtech%netbsd.org@localhost>]

Rather than going through and finding all the places where we added
"DragonFly" because it doesn't match "*BSD" in order to add Bitrig
(and maybe to exclude kFreeBSD?) ... and then doing it again for the
next schism, should we have something in the infrastructure that tells
us whether we're on a "BSD" platform?

By this I mean primarily NetBSD, FreeBSD, and their descendents and
offshoots; the idea is to be able to recognize all of these easily as
they share many properties -- that is, anything that will build for
both NetBSD and FreeBSD will probably also build (or can readily be
made to build) for all the others, but many of these things won't
build or run on Linux, Solaris, etc. without more substantial work.

The most likely use is in ONLY_FOR_PLATFORM, so I was originally
thinking of a *PLATFORMS variable (akin to LP64PLATFORMS) but this
isn't particularly tidy; it could also just be a plain variable set
differently as needed.

(Also, are there currently any such platforms we support beyond
NetBSD, FreeBSD, OpenBSD, DragonFly, MirBSD, Bitrig, and I guess also
BSD/OS?)


I am probably overthinking this as there are probably only a few dozen
places it really belongs, if that... most of the "add Dragonfly" stuff
appears in patches.

-- 
David A. Holland
dholland%netbsd.org@localhost