patch 8.0.1235: cannot disable the terminal feature in a huge build

Problem:    Cannot disable the terminal feature in a huge build. (lindhobe)
Solution:   Adjust the autoconf check. (Kazunobu Kuriyama, closes #2242)
diff --git a/src/configure.ac b/src/configure.ac
index f465096..2185c9e 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -2035,7 +2035,7 @@
 AC_MSG_CHECKING(--enable-terminal argument)
 AC_ARG_ENABLE(terminal,
 	[  --enable-terminal       Enable terminal emulation support.],
-	[enable_terminal="yes"], [enable_terminal="auto"])
+	, [enable_terminal="auto"])
 if test "$enable_terminal" = "yes" || test "$enable_terminal" = "auto" -a "x$features" = "xhuge" ; then
   if test "x$features" = "xtiny" -o "x$features" = "xsmall"; then
     AC_MSG_RESULT([cannot use terminal emulator with tiny or small features])