This is an auto-filled bug because dev-libs/crypto++ calls ar directly. The issue was originally discovered on arm64, but it may be reproducible on other arches as well. Attached build log and emerge --info. NOTE: To reproduce this issue you may want to temporarily move the /usr/bin/ar binary.
Created attachment 634090 [details] build.log build log and emerge --info
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=ec55c8d05afb50627a4b966628e6ee27e35f1fa4