Final(?) patch to update libtool in GCC and src trees

[Paolo Bonzini]

> This feels backwards to me.
> 
> I think we should do a Src tree only patch (GCC tree doesn't need this
> change) to set ACLOCAL_AMFLAGS and to remove the use of sinclude before
> doing anything else with libtool.

It might be, but I was just trying to be helpful and make the libtool 
patch as small (and easy to maintain as possible).  Other cleanups, 
while much appreciated, are tangential.

(Besides, I am going on vacation on the 22nd and wanted to get the patch 
in before that!)

Paolo