instead of using a $(VARS_TO_PASS) write the variables into a
*.mk include file, so that people can cd to some package direc-
tory and invoke gmake directly
fake OpenBSD as uname for MirBSD, so that we get a little further
in the build process there (stops at linux requiring bash now)
Tested with a full build (standard config) on Linux.
Invoking gmake in a subdirectory *not* tested, but
that didn't work before at all, so it's not a problem.