Add "getdeps" target to predownload all the deps.

Makefile

@@ -322,4 +322,7 @@ $(APPIMAGE_OUTPUT): installdir/AppRun installdir/love.desktop installdir/love.sv
 	./appimagetool installdir2 love-master.AppImage
 	rm -rf installdir2
 
+getdeps: cmake_install.sh appimagetool $(SDL2_PATH)/configure $(LIBOGG_FILE).tar.gz $(LIBVORBIS_FILE).tar.gz $(LIBTHEORA_FILE).tar.gz $(ZLIB_PATH)/configure $(LIBPNG_FILE).tar.gz $(BROTLI_PATH)/CMakeLists.txt $(BZIP2_FILE).tar.gz $(FT_FILE).tar.gz $(MPG123_FILE).tar.bz2 $(LIBMODPLUG_FILE).tar.gz $(LUAJIT_PATH)/Makefile $(LOVE_PATH)/CMakeLists.txt
+
 .DEFAULT_GOAL := $(APPIMAGE_OUTPUT)
+.PHONY := getdeps