compiler.pri: add OpenBSD.
compiler.pri: add OpenBSD.

Handle OpenBSD like we do FreeBSD:

1. Add /usr/local/lib to QMAKE_LIBDIR
2. Add /usr/local/include to INCLUDEPATH
3. Ensure we prefer /usr/lib over /usr/local/lib

Point 3 is mostly for FreeBSD, where we use the
base system's OpenSSL because the Qt port uses that.
This is to ensure both Mumble and Qt use the same
versions of libssl and libcrypto. If we mix-and-match,
we'll crash.

Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble