Updating top-level autoconf to 2.59

[Ian Lance Taylor]

Paolo Bonzini <paolo.bonzini@lu.unisi.ch> writes:

> 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.

That works for me too.  I don't think the current rules taken as a
whole make much sense.  Although it would imply delaying gcc's
transition to current autoconf versions.

Ian