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/main.c b/src/main.c
index 0283231..97f1b03 100644
--- a/src/main.c
+++ b/src/main.c
@@ -299,7 +299,7 @@
 	params.want_full_screen = FALSE;
 #endif
 
-#if defined(FEAT_GUI_MAC) && defined(MACOS_X_UNIX)
+#if defined(FEAT_GUI_MAC) && defined(MACOS_X_DARWIN)
     /* When the GUI is started from Finder, need to display messages in a
      * message box.  isatty(2) returns TRUE anyway, thus we need to check the
      * name to know we're not started from a terminal. */
@@ -927,13 +927,6 @@
     qnx_init();		/* PhAttach() for clipboard, (and gui) */
 #endif
 
-#ifdef MAC_OS_CLASSIC
-    /* Prepare for possibly starting GUI sometime */
-    /* Macintosh needs this before any memory is allocated. */
-    gui_prepare(&paramp->argc, paramp->argv);
-    TIME_MSG("GUI prepared");
-#endif
-
     /* Init the table of Normal mode commands. */
     init_normal_cmds();
 
@@ -984,7 +977,7 @@
 #ifdef FEAT_SUN_WORKSHOP
     findYourself(paramp->argv[0]);
 #endif
-#if defined(FEAT_GUI) && !defined(MAC_OS_CLASSIC)
+#if defined(FEAT_GUI)
     /* Prepare for possibly starting GUI sometime */
     gui_prepare(&paramp->argc, paramp->argv);
     TIME_MSG("GUI prepared");
@@ -1724,7 +1717,7 @@
 
     initstr = gettail((char_u *)parmp->argv[0]);
 
-#ifdef MACOS_X_UNIX
+#ifdef FEAT_GUI_MAC
     /* An issue has been seen when launching Vim in such a way that
      * $PWD/$ARGV[0] or $ARGV[0] is not the absolute path to the
      * executable or a symbolic link of it. Until this issue is resolved
@@ -2619,7 +2612,7 @@
 #if defined(HAS_SWAP_EXISTS_ACTION)
     check_swap_exists_action();
 #endif
-#if !(defined(AMIGA) || defined(MACOS))
+#if !(defined(AMIGA) || defined(MACOS_X))
     /*
      * Close stdin and dup it from stderr.  Required for GPM to work
      * properly, and for running external commands.