* lib/autoconf/c.m4 (_AC_PROG_PREPROC_WORKS_IFELSE): Remove

* lib/autoconf/c.m4 (_AC_PROG_PREPROC_WORKS_IFELSE): Remove
comment about ac_cpp_err; it was incorrect, and anyway
ac_cpp_err is being removed below.
* lib/autoconf/general.m4 (_AC_PREPROC_IFELSE): Don't
set ac_cpp_err to 'yesyes' if preproc_warn_flag and werror_flag
are both 'yes'.  In fact, don't bother setting ac_cpp_err at all;
nobody uses it.
(_AC_COMPILE_IFELSE, _AC_LINK_IFELSE): Don't log our funky tests
with werror_flag and conftest.err and so forth.  This is more
compatible with how _AC_PROG_PREPROC_WORKS_IFELSE behaves,
and anyway the user shouldn't normally want to see this gorp logged.
Problem reported by Ralf Wildenhues.
* lib/autoconf/lang.m4 (AC_LANG_WERROR): werror_flag's default is
empty, not 'no', since the rest of the code uses 'test -z'.