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/pty.c b/src/pty.c
index 151a278..1a27ab6 100644
--- a/src/pty.c
+++ b/src/pty.c
@@ -89,7 +89,7 @@
 # include <sys/ptem.h>
 #endif
 
-#if !defined(SUN_SYSTEM) && !defined(VMS) && !defined(MACOS)
+#if !defined(SUN_SYSTEM) && !defined(VMS)
 # include <sys/ioctl.h>
 #endif
 
@@ -379,21 +379,15 @@
     {
 	for (d = PTYRANGE1; (p[1] = *d) != '\0'; d++)
 	{
-#if !defined(MACOS) || defined(USE_CARBONIZED)
 	    if ((f = open(PtyName, O_RDWR | O_NOCTTY | O_EXTRA, 0)) == -1)
-#else
-	    if ((f = open(PtyName, O_RDWR | O_NOCTTY | O_EXTRA)) == -1)
-#endif
 		continue;
 	    q[0] = *l;
 	    q[1] = *d;
-#ifndef MACOS
 	    if (geteuid() != ROOT_UID && mch_access(TtyName, R_OK | W_OK))
 	    {
 		close(f);
 		continue;
 	    }
-#endif
 #if defined(SUN_SYSTEM) && defined(TIOCGPGRP) && !defined(SUNOS3)
 	    /* Hack to ensure that the slave side of the pty is
 	     * unused. May not work in anything other than SunOS4.1