patch 8.0.1236: Mac features are confusing

Problem:    Mac features are confusing.
Solution:   Make feature names more consistent, add "osxdarwin". Rename
            feature flags, cleanup Mac code. (Kazunobu Kuriyama, closes #2178)
diff --git a/src/termlib.c b/src/termlib.c
index fee14ae..0dc5894 100644
--- a/src/termlib.c
+++ b/src/termlib.c
@@ -13,7 +13,7 @@
 #include "vim.h"
 #include "termlib.pro"
 
-#if !defined(AMIGA) && !defined(VMS) && !defined(MACOS)
+#if !defined(AMIGA) && !defined(VMS)
 # include <sgtty.h>
 #endif