CPython checks for stdarg.h as HAVE_STDARG_PROTOTYPES
at some places
but not at other places
. Either this check should be repeated at every call site or should be removed all together, most compilers supports this nowadays (should be verified with buildbots).
cc
Footnotes
https://github.com/python/cpython/blob/16a7e4a0b75080275bf12cfb71d54b01d85099b2/configure.ac#L5026
https://github.com/python/cpython/blob/16a7e4a0b75080275bf12cfb71d54b01d85099b2/Objects/call.c#L557