Allow iov_base as char * on Solaris 8/9/10.

On Solaris 8, 9, 10/SPARC, iov_base is of type caddr_t which is char *. The Sun C++ compiler errors with "Cannot assign void* to char*". Using a static case to override this. On Solaris 11, HP-UX, AIX, and RHEL, iov_base is void * so no issues there. This seems a rather hackish solution so open to something better.