both freebsd-gcc6@amd64 and @i386 builds fine on amd64, @i386 also builds fine on i386. I didn't try @amd64 on i386, but I see no reason it shouldn't work.

I'm wrong in that you can remove char cupsfilter completely from options.c, I misread the code the first time.

So, I've just had a quick look at the code.
char cupsfilter is defined in foomaticrip.c, and also options.c (which this patch changes). It is also declared in foomaticrip.h. I think it should be enough to remove it completely from options.c, since options.c includes foomaticrip.h.
I'm testing the build currently, but it will take a bit of time. I'll let you know once I'm done.

Interestingly, I have acpi_video in my kernel, and I've never had any issues with this, even though acpi_video attaches long before the DRM kernel modules.