It turns out that qemumips64 has bitrotted and libtool no longer works. We'd know about this if it were being built on the autobuilder.
http://git.yoctoproject.org/cgit/cgit.cgi/yocto-autobuilder/commit/buildset-config.controller/nightly-mips64.conf?id=8cd5383b92b69013ff16ee174d2c081d677c5d37