* configure.ac: Fix typo. Reported by Juri Linkov
<juri@linkov.net>.
passthrough="$passthrough --with-mailutils=$with_mailutils"
passthrough="$passthrough --with-pop=$with_pop"
passthrough="$passthrough --with-harfbuzz=$with_harfbuzz"
- passthrough="$passthrough --with-threads=$with_png"
+ passthrough="$passthrough --with-threads=$with_threads"
# Now pass through some checking options.
emacs_val="--enable-check-lisp-object-type=$enable_check_lisp_object_type"