supporting these features with cross building is non-trivial
and they do are generally not useful features, so remove them.
as result the abuildrepo is also removed to write out paths.
all package generation paths now use $REPODEST/$repo/$CARCH
which allows easily writing packages to correct $subpkgarch
in future commits.

flock(2) on an NFS mount will on the server side convert the lock to a
POSIX lock (fcntl(F_SETLK)). This means that abuild running on NFS
server and client will create different locks and they will both try
download same file at same time.

We fix this by creating a small abuild-fetch application that will
create a POSIX lock which works with NFS.