Redefining it as a typedef is an error, as it prevents overloading
on e.g., int/wchar_t separately.

__null is a magic constant of integral type that converts to a null pointer
as should be, but warns for ambiguity when used to resolved an overload
between an integral type and a pointer type.

entire trees for testing anyway, I might as well do this intrusive touching
of include files now.  Added openBSD tags.