gentoo-overlay/sci-mathematics/msieve/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "https://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <!-- maintainer-needed -->
  <use>
    <flag name="ecm">Enable support for the GMP-ECM library</flag>
  </use>
  <upstream>
    <remote-id type="sourceforge">msieve</remote-id>
  </upstream>
</pkgmetadata>