This is an auto-filed bug because sys-fs/xfsprogs misses USE=static-libs and installs '.a' files.
The issue was originally discovered on amd64, but it may be reproducible on other arches as well.
The issue was discovered on the version reported in the summary but it may be reproducible on other versions as well. The best solution is avoid to build the '.a' files by touching the configure. In case the buildsystem makes your life hard, a good compromise would be just remove the files.
NOTE: If you want to change the summary, to avoid auto-filed duplicates, please at least keep the word 'static-libs'
USE=static-libs was intentionally dropped, see https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=2b3b60e6ad3756c422e0f304150419217d2478fb
We decided to keep the created .a file because it's pointless to throw it away after spending some amount of time/CPU cycles to build it now that we can no longer avoid it.
*** Bug 725570 has been marked as a duplicate of this bug. ***
I'm re-opening this because a QA policy on this has been documented (somewhat recently I assume).