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/term.c b/src/term.c
index 4a202bb..8df5e02 100644
--- a/src/term.c
+++ b/src/term.c
@@ -2534,7 +2534,7 @@
     void
 out_char(unsigned c)
 {
-#if defined(UNIX) || defined(VMS) || defined(AMIGA) || defined(MACOS_X_UNIX)
+#if defined(UNIX) || defined(VMS) || defined(AMIGA) || defined(MACOS_X)
     if (c == '\n')	/* turn LF into CR-LF (CRMOD doesn't seem to do this) */
 	out_char('\r');
 #endif
@@ -2554,7 +2554,7 @@
     static void
 out_char_nf(unsigned c)
 {
-#if defined(UNIX) || defined(VMS) || defined(AMIGA) || defined(MACOS_X_UNIX)
+#if defined(UNIX) || defined(VMS) || defined(AMIGA) || defined(MACOS_X)
     if (c == '\n')	/* turn LF into CR-LF (CRMOD doesn't seem to do this) */
 	out_char_nf('\r');
 #endif