scripts/install_tinyxml2: try to use wget if curl is not available

pushd "build-$pkgname"

if [[ ! -f "$pkgver.tar.gz" ]]; then

    if [[ $(command -v curl) ]]; then

        curl -gqb "" -fLC - --retry 3 --retry-delay 3 -o "$pkgver.tar.gz" "$url"

    elif [[ $(command -v wget) ]]; then

        wget -q --no-glob --no-config --continue --tries=3 --waitretry=3 -O "$pkgver.tar.gz" "$url"

    else

        echo "Error: none of curl and wget is available, cannot proceed." >&2

        echo "You can install either curl or wget in your system and try again." >&2

        echo "(Or install the tinyxml2 library (libtinyxml2-dev on Ubuntu) so that using this script is not necessary.)" >&2

        exit 1

    fi

fi

echo -e "$sha256sum\t$pkgver.tar.gz" > "$pkgname.checksum"

sha256sum --check "$pkgname.checksum"