As summary, kde-base/kdegraphics failed to build on my machine telling me that app-text/poppler should be built again with QT use flag, but app-text/poppler doesn't have any QT flag :-) Instead, the correct error message should be to re-emerge app-text/poppler-bindings with QT flag
*** This bug has been marked as a duplicate of 119717 ***
Not exactly the same bug, the error message wasn't fixed on kdegraphics, while the test was.
Fixed anyway.