Fix RPATH when CMAKE_INSTALL_LIBDIR is not just lib
Fix RPATH when CMAKE_INSTALL_LIBDIR is not just lib

shikhar413/openmc,smharper/openmc,mit-crpg/openmc,liangjg/openmc,smharper/openmc,smharper/openmc,amandalund/openmc,mit-crpg/openmc,shikhar413/openmc,paulromano/openmc,shikhar413/openmc,mit-crpg/openmc,paulromano/openmc,paulromano/openmc,amandalund/openmc,paulromano/openmc,amandalund/openmc,walshjon/openmc,liangjg/openmc,liangjg/openmc,walshjon/openmc,walshjon/openmc,amandalund/openmc,mit-crpg/openmc,liangjg/openmc,smharper/openmc,shikhar413/openmc,walshjon/openmc