configure accepts the new option --enable-single-binary to build all the
selected programs in a single binary called "coreutils". The selected
programs can still be called directly using symlinks to "coreutils" or
shebangs with the option --coreutils-prog= passed to this program. The
install behavior is determined by the option --enable-single-binary=symlinks
or --enable-single-binary=shebangs (the default).