Install this package:
emerge -a sys-cluster/native-mpi
<pkgmetadata> <maintainer type="person"> <email>alexxy@gentoo.org</email> <name>Alexey Shvetsov</name> </maintainer> <maintainer type="project"> <email>cluster@gentoo.org</email> <name>Gentoo Cluster Project</name> </maintainer> </pkgmetadata>