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/auto/configure b/src/auto/configure
index 4ee62b3..fa9276a 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -7475,7 +7475,7 @@
 $as_echo_n "checking --enable-terminal argument... " >&6; }
 # Check whether --enable-terminal was given.
 if test "${enable_terminal+set}" = set; then :
-  enableval=$enable_terminal; enable_terminal="yes"
+  enableval=$enable_terminal;
 else
   enable_terminal="auto"
 fi