PATCH: Fix build when NULL == nullptr_t

[Brian Callahan]

Hello --

As we previously discussed, there are potential build failures
in the case where a system chooses to define NULL as nullptr_t
when compiling C++11 or later. This is valid according to the
C++ spec. However, it causes all sorts of GM2 build failures.

The attached patch deals with this possibility and allows GM2
to build correctly on these systems. I chose the solution of
special-casing these systems, which is just OpenBSD at the
moment but may expand to include other systems.

The latest gm2-master builds and works correctly on OpenBSD
with this.

Thanks.

~Brian

gm2-fixNullptrT.diff
Description: Binary data