automake: remove support for threaded execution

automake: remove support for threaded execution

First, It add lots of complexity to the Automake script, which might
get in the way of future refactorings.

Also, the performance enhancements it offers seems to be fairly
limited:
<http://lists.gnu.org/archive/html/automake/2009-11/msg00004.html>
albeit not excessively so:
<http://www.open-mpi.org/community/lists/devel/2010/09/8524.php>

In the end, the most relevant reason for this change is that we want to
reach a point, during the yet-to-come maturity of Automake-NG, where it
will be just a thin layer around the provided scripts and makefile
fragments (with just a *tiny* smattering of preprocessing), as well as
around autom4te (for the proper parsing of configure.ac).  At such a
point, a threaded execution would bring no real benefit.

Oh, and we should really be pushing peoples towards non-recursive
build systems, where they just have one 'Makefile.am', and thus
threading on different 'Makefile.am's is irrelevant ;-)

* NG-NEWS: Update.
* doc/automake-ng.texi, NG-NEWS: Likewise.
* configure.ac: Don't check for 'ithreads' support in perl.
Drop AC_SUBST 'PERL_THREADS'.
* bootstrap.sh (PERL_THREADS): Don't define.
(dosubst): Don't substitute it.
* lib/Automake/Config.in ($perl_threads): Define no more.
(@EXPORT): Drop it.
* aclocal.in ($perl_threads): Remove, no more needed.
* automake.in (BEGIN) [$perl_threads]: Don't require nor import
the 'threads' and 'Thread::Queue' modules.
(QUEUE_MESSAGE, QUEUE_CONF_FILE, QUEUE_LOCATION, QUEUE_STRING):
Delete constants.
($required_conf_file_queue): Delete variable.
($nthreads): Likewise, and thus ...
(get_number_of_threads): ... delete this function, whose only
purpose was to initialize that variable.
(handle_makefiles_serial): Delete, its body inlined in the main
code.
(require_file_internal): Don't take the '$QUEUE' argument, nor
handle threading/serialization calling back ...
(queue_required_file_check_or_copy): ... this function, which
has thus been removed.
(require_libsource_with_macro): Adjust 'require_file_internal'
call to new signature.
(require_conf_file): Likewise, in the process dropping any
handling of threading/serialization.
(handle_makefiles_threaded): This is no more called anywhere,
so delete it, together with ...
(require_queued_file_check_or_copy): ... this, which has in
that its only caller.
* lib/Automake/Location.pm (serialize, deserialize): Delete
as unused.
* lib/Automake/Channels.pm (setup_channel_queue,
pop_channel_queue): Likewise.
(@EXPORT): Adjust.
(BEGIN) [$perl_threads]: Don't require nor import 'threads'.
(%_default_options): Remove 'ordered', 'queue' and 'queue_key'
keys, that were only required for serialization during threaded
Automake.
(_merge_options, _print_message): No need to handle those
options.
Adjust creation of channels 'automake', 'verb' and 'fatal'.
(_enqueue, _dequeue): Delete as unused.
(msg): Adjust a comment.
(verb): Don't try to display informations about the current
thread.
* lib/Automake/DisjConditions.pm (CLONE): Delete, no more
needed.
* t/ax/am-test-lib.sh (require_tool): Drop handing of
requirement 'perl-threads'; it is not used by any test now.
* t/parallel-am.sh: Remove as obsolete.
* t/parallel-am2.sh: Likewise.
* t/parallel-am3.sh: Likewise.
* t/pm/Condition-t.pl: Likewise.
* t/pm/DisjConditions-t.pl: Likewise.
* Makefile.am (check-coverage-run, recheck-coverage-run): Don't
export 'WANT_NO_THREADS' to "yes", nor unset 'AUTOMAKE_JOBS'.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>