This patch fixes LWG issue 2221 by adding a nullptr overload to basic_ostream.
We externally instantiate the rest of these methods, but we can't do that here (for backwards compat reasons).
You need to add _LIBCPP_INLINE_VISIBILITY and maybe put it at the bottom of the group because it's unique in this way.
inline or just define the thing inside the class.
But I'm not sure we want to forward to the const void* overload. My understanding of that overload is that it exists to print "bool" values for types like ostream that used to implement if (stream) via a conversion to void*.
I think we may just want to print nill.
I don't think this test is portable. Implementations can print null or nill or "hubbabalo" for that matter.
I suggested this approach to Zoe, because I thought that that was what GCC did. (print 0x0)