Patch to update top-level config to autoconf 2.59

[Paolo Bonzini]

> Yep.  Also, it would be best if you could test this change also on a 
> cross-compiler, a Canadian cross, and maybe even a host-x-host (i.e. 
> host != build, but build == target) configuration.  Be sure to use 
> non-canonical names (i.e. names that config.sub will change).  :-)
> 
> Personally I would not be against this change even if it breaks some 
> configurations, as long as it is known *which*.

... and why.  (And as long as there are plans to fix them -- I had in 
mind especially the non-canonical names).

Paolo