[Patch] Fix libstdc++/11378 (take2) + xsputn optmizations

[Paolo Carlini]

Benjamin Kosnik wrote:

>With lseek, I don't think there
>are as many options.
>
 From glibc2.3.2 info pages:

     When the source file is compiled with `_FILE_OFFSET_BITS == 64' the
     `lseek' function is in fact `lseek64' and the type `off_t' has 64
     bits which makes it possible to handle files up to 2^63 bytes in
     length.

 ;-)

Benjamin we are lucky!

Paolo.