This:

AC_CHECK_FILE(/dev/ptmx, AC_DEFINE(HAVE_DEV_PTMX, 1, [Define if we have /dev/ptmx.]))

Is being translated into:

echo "$as_me:$LINENO: checking for /dev/ptmx" >&5
echo $ECHO_N "checking for /dev/ptmx... $ECHO_C" >&6
if test "${ac_cv_file__dev_ptmx+set}" = set; then
  echo $ECHO_N "(cached) $ECHO_C" >&6
else
  test "$cross_compiling" = yes &&
  { { echo "$as_me:$LINENO: error: cannot check for file existence when cross compiling" >&5
echo "$as_me: error: cannot check for file existence when cross compiling" >&2;}
   { (exit 1); exit 1; }; }
if test -r "/dev/ptmx"; then
  ac_cv_file__dev_ptmx=yes
else
  ac_cv_file__dev_ptmx=no
fi
fi

Which exits when I do:

$ export CC_FOR_BUILD=gcc
$ sh configure --host=arm-eabi

With an error like:

checking for /dev/ptmx... configure: error: cannot check for file existence when cross compiling

I am using the latest version of msys/mingw with devkitarm to cross compile.  Is this supposed to happen?