This is an auto-filled bug because sys-apps/gawk calls ar directly.
The issue was originally discovered on s390, but it may be reproducible on other arches as well.
Attached build log and emerge --info.
If you think it doesn't make sense fix these type of issues, I'd like to point out that won't be possible use a different AR implementation (like llvm-ar) by setting the AR variable. So this issue has been reproduced by setting the AR variable to s390x-ibm-linux-gnu-ar and by removing the /usr/bin/ar binary.
Created attachment 635708 [details]
build log and emerge --info
Created attachment 641672 [details, diff]
Upstream merged it as https://git.savannah.gnu.org/cgit/gawk.git/commit/?id=47dce6a7002a8d7b818c19d574d81327b769871b