cc/gcc: CC_STATIC_LIBSTDCXX 'depends on' CONFIGURE_has_static_libstdcpp

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>

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