I just ran an "emerge --sync" and noticed that the ebuild file for libvirt changed.  Now I get a new result.  "Unexpected problems, indeed".  I will update my kernel and report back.

ostara ~ # ebuild /usr/portage/app-emulation/libvirt/libvirt-1.1.2-r1.ebuild setup clean
 * libvirt-1.1.2.tar.gz SHA256 SHA512 WHIRLPOOL size ;-) ...                                                       [ ok ]
 * libvirt-1.1.2-e89bdf01.tar.xz SHA256 SHA512 WHIRLPOOL size ;-) ...                                              [ ok ]
 * checking ebuild checksums ;-) ...                                                                               [ ok ]
 * checking auxfile checksums ;-) ...                                                                              [ ok ]
 * checking miscfile checksums ;-) ...                                                                             [ ok ]
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found kernel object directory:
 *     /lib/modules/3.10.7-gentoo/build
 * Found sources for kernel version:
 *     3.10.7-gentoo
 * Checking for suitable kernel configuration options...
 *   CONFIG_SECURITYFS:  is not set when it should be.
 * Please check to make sure these options are set correctly.
 * Failure to do so may cause unexpected problems.