I don't know if this is a quirk of our build system (Chromium OS) but I don't think so because we are using the standard Gentoo ebuild for util-linux. This applies to sys-apps/util-linux-2.16.2 when cross-compiling for arm. When emerging sys-apps/util-linux in isolation, econf fails with this error: configure: error: cramfs selected but libz not found Manually emerging sys-libs/zlib fixed this problem. So it looks like a missing dependency. I am available for follow-up if this information is not enough. (If it matters, I was emerging xfsprogs when this problem came up, and I had done no previous emerges for arm, so nothing was installed in the sysroot yet.)
OK sorry, we have an ancient version and it looks like this has been fixed already.