Message 283093 - Python tracker

> And would be nice to extend the optimization to C functions.

I tried it but skipping creating PyCFunction seems impossible for now.

My current idea is adding new `tp_fastcall` slot which has same signature
to _PyFunction_FastCallDict or _PyCFunction_FastCallDict.

If MethodDescrObject implement it, we can skip temporary PyCFunction object and
argument tuple.

But I think it should be separated issue. Patch is large enough already.