Support setting compilation options by string

[eyalroz]

It would be nice if compilation options could be set using a string, as we might see it in the render options, e.g. being able to say something like options.set("--device-int128") do the equivalent of options.support_128bit_integers = true and options.set("--language_dialect=c++17") do the equivalent of options.set_language_dialect(cpp17).