Change how we handle options required by 'way's
We used to add the options when the way was enabled, but this caused problems with the static/dynamic choice, as once the 'dynamic' options had been added it wasn't easy to remove them. We therefore didn't allow -static on the commandline if we'd already seen -static, which kludged around the issue. But apart from being unsatisfactory in the first place, this is a problem if we want to allow -dynamic being on by default, as there wouldn't be any way to turn it off. So now we add C/CPP/linker flags required by the 'way's when flags are requested, rather than during flag parsing.