gentoo-overlay/sys-apps/baselayout-prefix/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "https://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<maintainer type="project">
	<email>prefix@gentoo.org</email>
</maintainer>
<use>
	<flag name="split-usr">Enable this if /bin and /usr/bin are separate directories</flag>
</use>
</pkgmetadata>