* QA Notice: Unrecognized configure options:
I could be misinterpreting but seems the dxva2 patchset is in process of being upstreamed to vanilla wine and was disabled to avoid conflicts, however I don't think the support is complete in wine-5.12 (no configure option, and doesn't seem to check for libva).
Sources: wine-staging definition file, and wine-5.12 changelog has dxva2 mentions.
For now I guess USE=vaapi should be removed or masked in 5.12.
*** Bug 742674 has been marked as a duplicate of this bug. ***