nullptr vs 0

From: Peter Dimov (pdimov_at_[hidden])
Date: 2022-05-22 00:59:20

Compilers apparently are warning on the use of 0 as a null pointer
constant, suggesting we use nullptr instead. But compilers don't know
that we support C++03 where nullptr isn't a thing.

Case in point: https://github.com/boostorg/throw_exception/pull/22

ifdef-ing every use of nullptr is unwieldy, so maybe we need
BOOST_NULLPTR added to Boost.Config? That would expand to
nullptr when it's supported, and 0 otherwise.