Ports/file: Build host version to ensure we can properly cross compile

[supercomputer7]

We should build file natively as well so it can be used to compile the target build (for serenity). The Makefile doesn't do this automatically so to ensure it will not fail due to version mismatch between the host version and target version, we ensure we always have a native binary at hand.

Some funny backstory - I looked on the Internet something related to bashisms and dash, and was interested to see the state of the dash port, and (surprise surprise) I saw it did the host_env trickery @timschumi suggested to do and simply copied the procedures and changed it a bit to work according to the README.DEVELOPER guidelines in the port.

Closes #18415.

[timschumi]

Dash really isn't the best example regarding the ports script code quality, we have since found better ways to express certain constructs. I'd recommend something like the following instead (untested, but you get the idea):

function pre_configure() {
    host_env
    mkdir -p "host-build"
    (
        cd host-build
        "../${workdir}/configure"
        make
    )
    target_env  # Not sure if this is required
}

export FILE_COMPILE_DEP="${PORT_BUILD_DIR}/host-build/src/file"

This allows us to keep the target build steps unchanged, and doesn't add as much subshell boilerplate code.