Resize unamebuf[] to avoid warnings about snprintf() not having
requested to merge 1965-bin-named-unix-os-c-warning-s-directive-output-may-be-truncated-on-openindiana-v9_11 into v9_11
enough buffer space. Also change named_os_uname() prototype so that it is now returning (const char *) rather than (char *). If uname() is not supported on a UNIX build prepopulate unamebuf[] with "unknown architecture".
(cherry picked from commit 4bc3de07)
Closes #1965 (closed)