QNX support for qremoteobjects fails to build with newer C++ standards

In a few places a const pointer is assigned to the iov_base field of the iov_t structure, which is of type void *. Newer C++ does not allow such an assignment.

QNX 7.1 addressed that by adding a iov_base_const field to the structure and providing a SETIOV_CONST macro, but for 7.0 there needs to be some way to define this locally (see the proposed patch - ugly, but works).