amarok 1.90-r1 fails to build, I'll attach the build log. Reproducible: Always
Created attachment 174622 [details] emerge --info
Created attachment 174624 [details] amarok-1.90-r1/temp/build.log
Do you have qt-opengl ?
But it seems you're right - ebuild does lack a qt-opengl dep.
Fix added to the tree. Thanks for report.