[Bug c++/60760] arithmetic on null pointers should not be allowed in constant expressions

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60760

--- Comment #8 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch resubmitted for review:
https://gcc.gnu.org/ml/gcc-patches/2016-05/msg00935.html