This fixes issues where a new option is added, an option is removed, the
constraints of an option are changed, an option file is added where one
didn't previously exist, an option file is deleted, or it is renamed
between meson_options.txt and meson.options
There is one case that is known to not work, but it's probably a less
common case, which is setting options for an unconfigured subproject.
We could probably make that work in some cases, but I don't think it
makes sense to download a wrap during meson configure.