The libcap-ng recipe in meta-security has libcap in its DEPENDS, but as far as I can tell it should effectively be a replacement for libcap. I don't see a check in the libcap-ng configure script for it, and neither the Fedora spec file nor the Debian package info mention libcap as a build dependency of libcap-ng, so it's likely bogus.
Changes pushed at: http://git.yoctoproject.org/cgit.cgi/poky-contrib/log/?h=mulhern/bug5084.
Changes at: http://git.yoctoproject.org/cgit/cgit.cgi/meta-security/commit/?id=acf8d44f706ab9682d294fabe31ca04486e8fe5a.