$ sudo emerge -u system
Calculating system dependencies... done!

>>> Emerging (1 of 4) sys-libs/glibc-2.4-r3 to /
 * glibc-libidn-2.4.tar.bz2 MD5 ;-) ...                                                                                                                                                  [ ok ]
 * glibc-libidn-2.4.tar.bz2 RMD160 ;-) ...                                                                                                                                               [ ok ]
 * glibc-libidn-2.4.tar.bz2 SHA1 ;-) ...                                                                                                                                                 [ ok ]
 * glibc-libidn-2.4.tar.bz2 SHA256 ;-) ...                                                                                                                                               [ ok ]
 * glibc-libidn-2.4.tar.bz2 size ;-) ...                                                                                                                                                 [ ok ]
 * glibc-2.4.tar.bz2 MD5 ;-) ...                                                                                                                                                         [ ok ]
 * glibc-2.4.tar.bz2 RMD160 ;-) ...                                                                                                                                                      [ ok ]
 * glibc-2.4.tar.bz2 SHA1 ;-) ...                                                                                                                                                        [ ok ]
 * glibc-2.4.tar.bz2 SHA256 ;-) ...                                                                                                                                                      [ ok ]
 * glibc-2.4.tar.bz2 size ;-) ...                                                                                                                                                        [ ok ]
 * glibc-ports-2.4.tar.bz2 MD5 ;-) ...                                                                                                                                                   [ ok ]
 * glibc-ports-2.4.tar.bz2 RMD160 ;-) ...                                                                                                                                                [ ok ]
 * glibc-ports-2.4.tar.bz2 SHA1 ;-) ...                                                                                                                                                  [ ok ]
 * glibc-ports-2.4.tar.bz2 SHA256 ;-) ...                                                                                                                                                [ ok ]
 * glibc-ports-2.4.tar.bz2 size ;-) ...                                                                                                                                                  [ ok ]
 * glibc-2.4-patches-1.17.tar.bz2 MD5 ;-) ...                                                                                                                                            [ ok ]
 * glibc-2.4-patches-1.17.tar.bz2 RMD160 ;-) ...                                                                                                                                         [ ok ]
 * glibc-2.4-patches-1.17.tar.bz2 SHA1 ;-) ...                                                                                                                                           [ ok ]
 * glibc-2.4-patches-1.17.tar.bz2 SHA256 ;-) ...                                                                                                                                         [ ok ]
 * glibc-2.4-patches-1.17.tar.bz2 size ;-) ...                                                                                                                                           [ ok ]
 * glibc-powerpc-cpu-addon-v0.01.tgz MD5 ;-) ...                                                                                                                                         [ ok ]
 * glibc-powerpc-cpu-addon-v0.01.tgz RMD160 ;-) ...                                                                                                                                      [ ok ]
 * glibc-powerpc-cpu-addon-v0.01.tgz SHA1 ;-) ...                                                                                                                                        [ ok ]
 * glibc-powerpc-cpu-addon-v0.01.tgz SHA256 ;-) ...                                                                                                                                      [ ok ]
 * glibc-powerpc-cpu-addon-v0.01.tgz size ;-) ...                                                                                                                                        [ ok ]
 * glibc-linuxthreads-20060605.tar.bz2 MD5 ;-) ...                                                                                                                                       [ ok ]
 * glibc-linuxthreads-20060605.tar.bz2 RMD160 ;-) ...                                                                                                                                    [ ok ]
 * glibc-linuxthreads-20060605.tar.bz2 SHA1 ;-) ...                                                                                                                                      [ ok ]
 * glibc-linuxthreads-20060605.tar.bz2 SHA256 ;-) ...                                                                                                                                    [ ok ]
 * glibc-linuxthreads-20060605.tar.bz2 size ;-) ...                                                                                                                                      [ ok ]
 * checking ebuild checksums ;-) ...                                                                                                                                                     [ ok ]
 * checking auxfile checksums ;-) ...                                                                                                                                                    [ ok ]
 * checking miscfile checksums ;-) ...                                                                                                                                                   [ ok ]
 * checking glibc-2.4.tar.bz2 ;-) ...                                                                                                                                                    [ ok ]
 * checking glibc-ports-2.4.tar.bz2 ;-) ...                                                                                                                                              [ ok ]
 * checking glibc-libidn-2.4.tar.bz2 ;-) ...                                                                                                                                             [ ok ]
 * checking glibc-2.4-patches-1.17.tar.bz2 ;-) ...                                                                                                                                       [ ok ]
 * checking glibc-linuxthreads-20060605.tar.bz2 ;-) ...                                                                                                                                  [ ok ]
 * checking glibc-powerpc-cpu-addon-v0.01.tgz ;-) ...                                                                                                                                    [ ok ]
 * glibc-2.4 is nptl-only!
 * NPTL requires a CHOST of i486 or better

!!! ERROR: sys-libs/glibc-2.4-r3 failed.
Call stack:
  ebuild.sh, line 1559:   Called dyn_setup
  ebuild.sh, line 666:   Called pkg_setup
  glibc-2.4-r3.ebuild, line 1079:   Called die

!!! please add USE='nptl nptlonly' to make.conf
!!! If you need support, post the topmost build error, and the call stack if relevant.