patch 8.0.0693: no terminal emulator support

Problem:    No terminal emulator support.  Cannot properly run commands in the
            GUI.  Cannot run a job interactively with an ssh connection.
Solution:   Very early implementation of the :terminal command.  Includes
            libvterm converted to ANSI C.  Many parts still missing.
diff --git a/src/config.h.in b/src/config.h.in
index a934507..fe68d49 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -431,6 +431,9 @@
 /* Define if you want to include process communication. */
 #undef FEAT_JOB_CHANNEL
 
+/* Define if you want to include terminal emulator support. */
+#undef FEAT_TERMINAL
+
 /* Define default global runtime path */
 #undef RUNTIME_GLOBAL