Produce warning for performing pointer arithmetic on a null pointer.
Summary:
Test and produce warning for subtracting a pointer from null or subtracting
null from a pointer. Reuse existing warning that this is undefined
behaviour. Also add unit test for both warnings.
Reformat to satisfy clang-format.
Respond to review comments: add additional test.
Respond to review comments: Do not issue warning for nullptr - nullptr
in C++.
Fix indenting to satisfy clang-format.
Respond to review comments: Add C++ tests.
Author: Jamie Schmeiser <schmeise@ca.ibm.com>
Reviewed By: efriedma (Eli Friedman), nickdesaulniers (Nick Desaulniers)
Differential Revision: https://reviews.llvm.org/D98798