boost: add use-tagged-layout option

The default value of '--layout=<layout>' on Unix is 'system', not 'tagged'.
We should follow the official default value.

from ./b2 --help

    --layout=<layout>       Determine whether to choose library names and header
                            locations such that multiple versions of Boost or
                            multiple compilers can be used on the same system.

                              -- versioned -- Names of boost binaries include
                              the Boost version number, name and version of
                              the compiler and encoded build properties. Boost
                              headers are installed in a subdirectory of
                              <HDRDIR> whose name contains the Boost version
                              number.

                              -- tagged -- Names of boost binaries include the
                              encoded build properties such as variant and
                              threading, but do not including compiler name
                              and version, or Boost version. This option is
                              useful if you build several variants of Boost,
                              using the same compiler.

                              -- system -- Binaries names do not include the
                              Boost version number or the name and version
                              number of the compiler. Boost headers are
                              installed directly into <HDRDIR>. This option is
                              intended for system integrators building
                              distribution packages.

                          The default value is 'versioned' on Windows, and
                          'system' on Unix.