Fixes the `AC_ARG_VAR' test failures.
* lib/autoconf/status.m4 (_AC_OUTPUT_FILES): Don't use cmp.
* lib/freeze.mk (check-forbidden-patterns): New.
* lib/autoconf/Makefile.am, lib/autotest/Makefile.am
* lib/m4sugar/Makefile.am (check-local): Use it to catch `cmp'.
* doc/autoconf.texi (Limitations of Usual Tools): HP-UX' cmp and
/dev/null.
Reported months ago by H. Merijn Brand.
* lib/autoconf/autoconf.m4: Include it.
* lib/autoconf/functions.m4: Use AN_FUNCTION for all the functions
that were listed in the original autoscan.list.
* lib/autoconf/headers.m4: Similarly with headers.
* lib/freeze.mk (autoconf_m4f_dependencies): Add autoscan.m4.
(.m4.m4f): Don't pass --prepend-include, since that's done by
tests/autom4te itself.
* lib/autoscan/Makefile.am: Include freeze.mk.
(autoscan.list): New target --this file is no longer a source.
(autoscan.pre): New file.