scripts: add script building AppImage based on portable build for Linux

scripts/build_appimage.sh

@@ -0,0 +1,51 @@
+#!/bin/sh
+
+APP=Xash3DFWGS
+ARCH=i686
+APPDIR=$APP.AppDir
+mkdir -p $APPDIR
+
+# Generate extras.pak
+python3 scripts/makepak.py extras.pak
+
+# Copy all needed files
+cp SDL2_linux/lib/libSDL2-2.0.so.0 $APPDIR/
+cp vgui-dev/lib/vgui.so $APPDIR/
+cp extras.pak $APPDIR/extras.pak
+cp build/engine/libxash.so \
+	build/mainui/libmenu.so \
+	build/vgui_support/libvgui_support.so \
+	build/game_launch/xash3d $APPDIR
+
+cat > $APPDIR/AppRun << 'EOF'
+#!/bin/sh
+
+echo "Xash3D FWGS installed as AppImage."
+
+ENGINEROOT=$(dirname -- "$(readlink -f -- "$0")")
+if [ -z "$XASH3D_BASEDIR" ]; then
+	export XASH3D_BASEDIR=$PWD
+fi
+export XASH3D_EXTRAS_PAK1="${ENGINEROOT}"/extras.pak
+export LD_LIBRARY_PATH="${ENGINEROOT}":$LD_LIBRARY_PATH
+${DEBUGGER} "${ENGINEROOT}"/xash3d "$@"
+exit $?
+EOF
+
+chmod +x $APPDIR/xash3d # Engine launcher
+chmod +x $APPDIR/AppRun # Engine launcher script
+
+wget "https://raw.githubusercontent.com/FWGS/fwgs-artwork/master/xash3d/icon_512.png" -O $APPDIR/$APP.png
+
+cat > $APPDIR/$APP.desktop <<EOF
+[Desktop Entry]
+Name=$APP
+Icon=$APP
+Type=Application
+Exec=AppRun
+Categories=Game;
+EOF
+
+wget "https://github.com/AppImage/AppImageKit/releases/download/continuous/appimagetool-$ARCH.AppImage"
+chmod +x appimagetool-$ARCH.AppImage
+./appimagetool-$ARCH.AppImage $APPDIR