Created attachment 701091 [details] build.log build.log attached. Looks to be related to some -Werror flag being enabled. Happens with -r1 too.
Duplicate of https://bugs.gentoo.org/673434 . There's 1.5.3-r3 which is stable for mainstream arches since 2019. Which reminded me to drop the old revisions. *** This bug has been marked as a duplicate of bug 673434 ***