attempt to fix BSD breakage

src/libcore/os.rs

@@ -375,7 +375,7 @@ pub fn self_exe_path() -> Option<Path> {
                            KERN_PROC as c_int,
                            KERN_PROC_PATHNAME as c_int, -1 as c_int];
                 sysctl(vec::raw::to_ptr(mib), vec::len(mib) as c_uint,
-                       buf, &mut sz, ptr::null(),
+                       buf as *mut c_void, &mut sz, ptr::null(),
                        0u as size_t) == (0 as c_int)
             }
         }