multilib: deprecate, will be moved to contrib

multilib: deprecate, will be moved to contrib

As of 2012-01-17, according to Google codesarch, almost no active
package is using the 'multilib' feature offered by automake.

The only major exception seems to be GCC...  But on a closer look,
it become clear that GCC basically carries its own version of
multilib support.  In fact, Automake syncs its 'config-ml.in' and
'symlink-tree' scripts from GCC; and the GCC repository contains a
version of the 'multi.m4' file that is *more* updated than the one
in the automake repository (the former having being modified the
last time in 2008, the latter only in 2006).

The 'multilib' feature was anyway hardly documented at all, only
being briefly cited in the manual as an "obscure feature", "still
experimental", that was only for users "familiar with multilibs"
and which "can debug problems they might encounter".  We expect
such users to be motivated and knowledgeable enough to make the
minor adjustments required to start using the contrib version of
multilib, if they really need to.

* NEWS (Future backward incompatibility): Update.
* doc/automake.texi: Deprecate multilib support.  State that it
will be removed from automake core in the next major release.
* m4/multi.m4 (AM_ENABLE_MULTILIB): Deprecate.  If called, now
gives a proper warning in the 'obsolete' category (while still
retaining its former behaviour for the rest).
* tests/multilib.test: Update.
* contrib/multilib/multi.m4: New, verbatim copy of the earlier
version of multi.m4, without the new deprecation warning.
* Makefile.am (fetch): Don't sync the 'config-ml.in' file nor
the 'symlink-tree' script from GCC SVN repository anymore.
(FETCHFILES): Adjust.
(WGET_GCC): Remove, it's not needed anymore.