chromeos-base/vm_tools/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<use>
	<flag name='kvm_host'>
    Build tools that run on the host system for managing VMs instead of
    building tools that run in the guest.
	</flag>
</use>
</pkgmetadata>