gentoo-overlay/sys-libs/libcxxrt/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <herd>bsd</herd>
  <maintainer>
    <email>aballier@gentoo.org</email>
    <name>Alexis Ballier</name>
  </maintainer>
  <use>
	  <flag name="libunwind">Use <pkg>sys-libs/libunwind</pkg> instead of libgcc_s for unwinding. This should allow avoiding relying on <pkg>sys-devel/gcc</pkg> but for now clang is setup to use libgcc_s.</flag>
  </use>
</pkgmetadata>