Compilation fails when off_t is defined as 32 bit integer

[nroi]

We are currently calling libc::sendfile with an offset of type i64. This works fine on machines where off_t is defined as a 64 bit signed integer, but it fails to compile on other machines (for example, ARM devices like the cubieboard or the Raspberry Pi: #14 (comment)).

Notice the following excerpt from man 2 sendfile:

The original Linux sendfile() system call was not designed to handle large file offsets. Consequently, Linux 2.4 added sendfile64(), with a wider type for the offset argument. The glibc sendfile() wrapper function transparently deals with the kernel differences.

By using sendfile64(), compilation should succeed on those devices that have off_t defined as a 32 bit signed integer.

[nroi]

The issue is solved with da1a3c1, but:

We are now using libc from our own libc repository (forked off the official libc repository). Obviously, we would prefer to use the official libc as dependency. Maybe we should contact the libc maintainers and see if they could include sendfile64(), so that we don't need our own fork.