Enable top-level recursive 'autoreconf'

[Hans-Peter Nilsson]

> From: Thomas Schwinge <thomas@codesourcery.com>
> Date: Thu, 19 Oct 2023 12:42:26 +0200

> It's just GCC and Binutils/GDB, or are the top-level files also shared
> with additional projects?

Not sure if that counts as "shared", but I regularly drop
in* newlib to build simulator targets (*-elf, *-newabi).
That's git://sourceware.org/git/newlib-cygwin.git but I
extract tarballs for the merging.

"Drop in" is actually the other way round, starting with a
newlib tarball, so gcc files overwrite newlib ones.

(FWIW, I never drop in binutils like that; they're better
built separately.  "Better" for your long-term sanity.)

brgds, H-P