TODO: remove some items

Those items have now been implemented:

- mingw32 target
we have it now, and even mingw64 too

- mingw32 host
it is certainly possible to canadian-build a toolchain to run
in a mingw host

- Cygwin host
it is possible to build a toolchain in Cygwin, and it is probably
possible to canadian-build it as well

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 # Compute s390-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

     if [ "${CT_ARCH_64}" = "y" ]; then

         CT_TARGET_ARCH="s390x${CT_ARCH_SUFFIX}"

     fi

 }