The existing ordering linked `libutil` before `libstore`, which causes
link failures when building statically. This is due to `libstore` using
functions from `libutil`, and the fact that symbol resolution works
"forward" - i.e. if you pass `-lfoo -lbar -lbaz`, any symbols that
`libbar` uses from `libbaz` will be resolved, but symbols from `libfoo`
will not since it comes first in the command line.
All this to say: this commit reorders the libraries which fixes the link
errors.
This is useful for one-off situations where you want to specify a
builder on the command line instead of having to mess with
nix.machines. E.g.
$ nix-build -A hello --argstr system x86_64-darwin \
--option builders 'root@macstadium1 x86_64-darwin'
will perform the specified build on "macstadium1".
It also removes the need for a separate nix.machines file since you
can specify builders in nix.conf directly. (In fact nix.machines is
yet another hack that predates the general nix.conf configuration
file, IIRC.)
Note: this option is supported by the daemon for trusted users. The
fact that this allows trusted users to specify paths to SSH keys to
which they don't normally have access is maybe a bit too much trust...
