Created attachment 210050 [details]
patch to graphics/opencv/Makefile
ports r520396 added option MFX. This depends on multimedia/intel-media-sdk which is only avaiable on x86.
I do not know enough about group OPTIONS to construct a patch to exclude it based on ARCH. This patch merely warns the user that they have selected something that is not supported. This is merely a foot-shooting prevention measure.
Over to committer of r520396 (the port has no maintainer).
See also ports r520395. Keeping track of ONLY_FOR_ARCHS changes in non-default dependencies doesn't scale and is error-prone. Only truly ARCH-specific options (e.g., SSE, NEON) makes sense to track in current port.
OpenCV itself doesn't limit MFX to x86, so if something else provides the same API it maybe possible to build. For example, VAAPI was initially x86-only.
Ideally, the framework should check ONLY_FOR_ARCHS, NOT_FOR_ARCHS, BROKEN, IGNORE, etc. in dependencies before starting build.