Fix ACX_LARGEFILE to use canonical host/target names

[Nick Clifton]

Hi Joseph,

> OK to commit this patch (GCC and src),
> with regeneration of the GDB and binutils configure scripts that use
> ACX_LARGEFILE?
> 
> 2009-11-20  Joseph Myers  <joseph@codesourcery.com>
> 
> 	* largefile.m4 (ACX_LARGEFILE): Require AC_CANONICAL_HOST and
> 	AC_CANONICAL_TARGET.

OK for binutils.

Cheers
   Nick