mini-freeze of autotools-governed files in GCC and src

[Kaveh R. Ghazi]

From: "Ralf Wildenhues" <Ralf.Wildenhues@gmx.de>

>> Why request developers ensure this and not bump the AC_PREREQ to make
>> sure?
>
> Toplevel config/override.m4 should already cause failure if you use
> anything other than Autoconf 2.64 (but it doesn't ensure Automake 1.11).

In addition to enforcing the version number, the AC_PREREQ in all the 
configure.ac files documents to the reader of the file what version to use. 
It's now out of date and a source of possible confusion.  I would suggest 
either (preferably) updating them all to 2.64 or removing them.