RFC: maint: c++: use nullptr for C++11

[Akim Demaille]

This patch addresses the newly introduced nullptr.

Paul, I would especially value your comments on this patch,
given your experience in portability issues.  Regardless
of taste issues (I can understand that YY_NULL looks disgraceful),
I am explicitly expecting NULL to be defined for C, but if
you think it's safer to define YY_NULL to ((void*) 0), please
just say so (I'd like to avoid that, since I've been told
many times that NULL needs not be 0, but I have just never
seen that, and given the idiom "if (cp)", I really wonder
if it does exist).

Not pushed, but it's in next now.  Will be pushed in 2.5.1,
and merged in master.

0004-c-use-nullptr-for-C-11.patch
Description: Binary data