I maually added ~amd64 to the ebuild for fvwm-2.5.8-r4, and it built with no problems, and has been running for a fortnight on my Acer Aspire 1501LMi notebook without problems, both under xfree96-4.3.99.902-r2 and now under xorg-x11-6.7.0.
2.5.8-r6 is now marked stable. Also marked rplay and libstroke deps stable.