[PATCH] Update libtool to latest git tip

[Paolo Bonzini]

> Well, libtool-2.2.6 is finally released (twice even).
> 
>> Actual approval depends on your answer to this question, but the patch is 
>> technically okay.  Can you commit it to the src repository too? There is 
>> some regeneration to do there too.
> 
> I know that GCC is now in stage 3, and that we missed the end of stage 1
> by a week, but I would still like to update gcc's libtool to 2.2.6.

It fixed a Darwin bug, right?

Paolo