yielding_select should be explicitly specified in ebuild in case of cross-compiling: checking if select yields when using pthreads... cross configure: error: crossing compiling: use --with-yielding_select=yes|no|manual
*** Bug 450528 has been marked as a duplicate of this bug. ***
Which value to set it to for your systems?
*** Bug 598696 has been marked as a duplicate of this bug. ***
should be fixed here: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=007731c32667ec22df59d8173b8b019229acb533