SystemInformation: Change GetRealAddress to return a size_t

The return value is not a real pointer, but an integer representing the offset of the symbol within the loaded binary/library (possibly including a load base). On CHERI, and thus Arm's Morello prototype, pointers are not just integers but are unforgeable hardware capabilities that contain additional metadata (including bounds and permissions) to provide fine-grained spatial safety. Casting a plain integer (in this case, a ptrdiff_t) to a void * gives a warning that we normally make fatal, as due to the unforgeability of capabilities it will not be a valid pointer, trapping on dereference. Whilst there are ways to squash this warning (typically by casting via (u)intptr_t), they are not appropriate here, since the return value does not need to be a void *, and are normally only needed for reusing void *-taking interfaces with a plain integer (e.g. pthread_create's void * argument). Thus change the return type to be size_t to represent that this is the non-negative integer offset of the address from the base address.

Note that, other than the dummy call in the constructor that throws away the result, this member function is unused.