Updating top-level autoconf to 2.59

[Paolo Bonzini]

>> * If you want to build an explicitly cross tool despite host == target, or 
>> act like you are cross compiling despite build == host, or build a native 
>> tool (i.e. one using the native directory layout and installed as plain 
>> "gcc") despite host != target, or act like you aren't cross compiling (so 
>> can run execute tests for $host) despite build != host, these should be 
>> determined by explicit configure options; not by which of build, host and 
>> target where specified explicitly and which were defaulted.  (And not by 
>> older autoconf's experiments to see if it can execute a program built for 
>> the host.)
> 
> I completely agree that this is how it should work.  Unfortunately,
> this is not how autoconf {2.x,x>13} works.  I don't agree with a
> number of the decisions made by the autoconf maintainers.  However, I
> do think that as long we use autoconf, there is some benefit to be
> gained by following autoconf's default behaviour.

My opinion is that *nobody* until now really used the autoconf 2.59 
rules; for GCC we were having them massaged by the toplevel.  If we want 
to change something, we should speak loud to the Autoconf maintainers.

Paolo