Credit: The initial Web Assembly cross compile was found in a pull request:
            #385
        by apowers313. The pull request was merged with some accompanying
        NetHack source tree integration changes in early October 2020.

Cross-compiler used: emscripten
Cross-compiler url: https://emscripten.org/docs/getting_started/downloads.html

    Here's a brief guide to obtaining the cross-compiler sources via git and
    building it on your system.

    For Ubuntu, the build prerequisite packages for building the compiler can
    be easily obtained:

        sudo apt-get install python3 cmake default-jre

    For macOS, you will need to install Xcode, git, cmake, Python 3.5 or new
    (at time of this writing).

    After installing the prerequite packages above, obtain the cross-compiler
    via git and build it from the directory of your choice using steps similar
    to these:

            git clone https://github.com/emscripten-core/emsdk.git
            cd emsdk
            git pull
            ./emsdk install latest
            ./emsdk activate latest
            source ./emsdk_env.sh

    The steps above reflect what was outlined at this url at the time
    of writing:

            https://emscripten.org/docs/getting_started/downloads.html

    That is the definitive source and trumps anything documented here.

    On your linux host, prepare to cross-compile NetHack as follows:

        cd sys/unix ; sh setup.sh hints/linux.2020 ; cd ../..
        make fetch-lua

    On your macOS host, prepare to cross-compile NetHack as follows:

        cd sys/unix ; sh setup.sh hints/macOS.2020 ; cd ../..
        make fetch-lua

    Then, cross-compile to targets/wasm as follows:

        make CROSS_TO_WASM=1

    You can build src/nethacklib.a from pull request 385 as follows:

        make WANT_LIBNH=1

    Do not add any additional windowport interfaces to your build
    (such as WANT_WIN_TTY=1 WANT_WIN_CURSES=1 WANT_WIN_X11=1 or
    WANT_WIN_QT=1) as those aren't applicable to the Web Assembly
    or nethacklib builds. A "shim" pseudo-windowport is included
    from pull request 385.

    Result: As mentioned, the wasm cross-compile will end up in
            targets/wasm and the nethacklib.a will end up
            src.

    The cross-compiler hints additions are enclosed inside ifdef sections
    and shouldn't interfere with the non-cross-compile builds using
    hints/linux.2020 or hints/macOS.2020.