re-use a previous build directory set up by
usage: fx use DIR or: fx --dir DIR use or: fx use Switches further `fx` commands to using a different build directory. This only works if `fx --dir DIR set ...` succeeded previously (and DIR has not been removed since). The next `fx build` or other such command will now refer to DIR. The previous build directory is left in place, so you can switch back again with `fx use` later. fx use without arguments will list the available build directories, naming the current active build directory (if any).