autoconf: error out if AC_OUTPUT receives more than three arguments

Modified versions of Autoconf exist that expect more than three
arguments to AC_OUTPUT; attempting to regenerate a configure
script that uses the extra arguments, with the unmodified
Autoconf, is likely to produce a broken script.

The feature enabled by a fourth argument, in the case I know about
(<https://invisible-island.net/autoconf/autoconf.html> - look for
“simplify the way we generate the config.h file”) is potentially
worth folding into our version of Autoconf, but we would need to
do it with a new AC_CONFIG_something macro, instead of reverting
to having AC_OUTPUT take arguments.

* lib/autoconf/status.m4 (AC_OUTPUT): Error out if more than three
  arguments are supplied.
* tests/torture.at: Add tests of AC_OUTPUT with one, three, and four
  arguments.  Two arguments is treated as a special case of three
  arguments, so it doesn’t need its own test.