Hide the staticaly linked libstdc++ option if the static libstdc++ is not
present, detected at configure time.
Add a blind option that says whether static linking is possible at all.
It defaults to 'y', but depends on the needed CONFIGURE_* options. For
now, it only depends on static libtdc++, but new dependencies can be
easily added.
Hide the global static toolchain option behind this new option.
Original patch by Bryan Hundven <bryanhundven@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>