This is an auto-filled bug because dev-lang/mercury fails tests.
The issue was originally discovered on amd64, but it may be reproducible on other arches as well.
If you think that a different summary clarifies the issue better, feel free to change it.
Attached build log and emerge --info.
If you need further logs, feel free to ask..
Created attachment 638812 [details]
build log and emerge --info