lib: Implement 'only' that creates a dependency chain from stdin
When building closed loops of packages you sometime don't want the
entire chain to be resolved to just figure out the order of 5 packages.
This implement --only
which resolves the chain and ensures only the
packages from stdin are included in the output chain.
This is useful for rebuild lists or when building tight loops of packages.
$ arch-rebuild-order -o cmake meson jsoncpp
meson jsoncpp cmake
$ arch-rebuild-order -o jsoncpp meson cmake
meson jsoncpp cmake
Signed-off-by: Morten Linderud morten@linderud.pw