Compilation of extension libraries written in C++ are reportedly
broken due to https://github.com/ruby/ruby/pull/2404
The root cause of this issue was that the definition of ANYARGS
differ between C and C++, and that of C++ is incompatible with the
updated ones.
We are using the incompatibility against itself. In C++ two distinct
function prototypes can be overloaded. We provide the old, ANYARGSed
prototypes in addition to the current granular ones; and let the
older ones warn about types.
