provide NO_LUA_RUNTIME build option

This option not only eliminates the Lua bindings, but also removes
the entire Lua runtime (admittedly the bindings are far larger than
the runtime, but if you're not using it...)

--- NO_LUA_RUNTIME=0 ---
% time make -j8
make -j8  132.84s user 11.28s system 704% cpu 20.455 total
% size sample-spaceship
   text    data     bss     dec     hex filename
4457128   20112   28640 4505880  44c118 sample-spaceship

--- NO_LUA_RUNTIME=1 ---
% time make -j8
make -j8  316.09s user 22.70s system 738% cpu 45.845 total
% size sample-spaceship
   text    data     bss     dec     hex filename
7470098   48080   29376 7547554  732aa2 sample-spaceship