Invalid C11 standard detection for _Static_assert

[Hirrolot]

It seems that we use ML99_PRIV_C11_VERSION prior to its definition:

metalang99/include/metalang99/priv/compiler_specific.h

Line 13 in 76ed225

#if __STDC__ && __STDC_VERSION__ >= ML99_PRIV_C11_VERSION

Therefore, it evaluates to 0, thus making the condition __STDC_VERSION__ >= ML99_PRIV_C11_VERSION invalid. This may result in emitting _Static_assert where it may not be supported (e.g., on C99).