Gentoo's Bugzilla –
Attachment 763856 Details for
Bug 832252dev-libs/libdispatch-5.4.2: /var/tmp/portage/dev-libs/libdispatch-5.4.2/work/swift-corelibs-libdispatch-swift-5.4.2-RELEASE/tests/dispatch_apply.c:58:27: error: variable 'j' set but not used [-Werror,-Wunused-but-set-variable]