Installing in, say /usr/lib64 can be accomplished with GNUInstalldirs if you specify cmake -DCMAKE_INSTALL_LIBDIR=lib64, which populates the CMAKE_INSTALL_FULL_LIBDIR variable with the appropriate prefix (also settable using -DCMAKE_INSTALL_PREFIX :-)
Use the value from GNUInstallDirs.
Installing in, say
/usr/lib64can be accomplished with GNUInstalldirs if you specifycmake -DCMAKE_INSTALL_LIBDIR=lib64, which populates theCMAKE_INSTALL_FULL_LIBDIRvariable with the appropriate prefix (also settable using-DCMAKE_INSTALL_PREFIX:-)