Update autotools version for gdb and binutils

[Matt Rice]

On Mon, May 7, 2018 at 7:30 PM, Alan Modra <amodra@gmail.com> wrote:
> *) The reason binutils-gdb and gcc share a top level dir, config, and
> most include files is to support combined tree builds.  I don't know
> how many people try to do that nowadays, and a combined tree build
> with --enable-maintainer-mode running autotools seems a little
> insane to me.

While i haven't done this in a few years, but i used to do so in the
not terribly distant past,
using git read-tree/$GIT_DIR to check out binutils/gcc/newlib into one
working directory,
when building for multiple os * architecture combos shared code then
only had to be built once,
plus it allowed me to maintain patches directly in git.