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/option.c b/src/option.c
index baa8d85..320bbfd 100644
--- a/src/option.c
+++ b/src/option.c
@@ -510,7 +510,7 @@
 #endif
 					    (char_u *)0L} SCRIPTID_INIT},
     {"antialias",   "anti", P_BOOL|P_VI_DEF|P_VIM|P_RCLR,
-#if defined(FEAT_GUI) && defined(MACOS_X)
+#if defined(FEAT_GUI_MAC)
 			    (char_u *)&p_antialias, PV_NONE,
 			    {(char_u *)FALSE, (char_u *)FALSE}
 #else
@@ -1431,7 +1431,7 @@
     {"guioptions",  "go",   P_STRING|P_VI_DEF|P_RALL|P_FLAGLIST,
 #if defined(FEAT_GUI)
 			    (char_u *)&p_go, PV_NONE,
-# if defined(UNIX) && !defined(MACOS)
+# if defined(UNIX) && !defined(FEAT_GUI_MAC)
 			    {(char_u *)"aegimrLtT", (char_u *)0L}
 # else
 			    {(char_u *)"egmrLtT", (char_u *)0L}
@@ -1697,8 +1697,7 @@
     {"isprint",	    "isp",  P_STRING|P_VI_DEF|P_RALL|P_COMMA|P_NODUP,
 			    (char_u *)&p_isp, PV_NONE,
 			    {
-#if defined(MSWIN) || (defined(MACOS) && !defined(MACOS_X)) \
-		|| defined(VMS)
+#if defined(MSWIN) || defined(VMS)
 			    (char_u *)"@,~-255",
 #else
 # ifdef EBCDIC
@@ -1989,7 +1988,7 @@
 #if defined(MSWIN)
 				(char_u *)"popup",
 #else
-# if defined(MACOS)
+# if defined(MACOS_X)
 				(char_u *)"popup_setpos",
 # else
 				(char_u *)"extend",
@@ -3650,7 +3649,7 @@
 		options[opt_idx].flags |= P_DEF_ALLOCED;
 	    }
 
-#if defined(MSWIN) || defined(MACOS) || defined(VMS)
+#if defined(MSWIN) || defined(MACOS_X) || defined(VMS)
 	    if (STRCMP(p_enc, "latin1") == 0
 # ifdef FEAT_MBYTE
 		    || enc_utf8