patch 8.0.1749: VMS: 100% CPU use, redefining mch_open() fails

Problem:    VMS: 100% CPU use, redefining mch_open() and mch_fopen() fails.
Solution:   Do not wait indefinitely in RealWaitForChar(). (Neil Rieck)
            Do not redefine mch_open() and mch_fopen() on VMS. (Zoltan
            Arpadffy)
diff --git a/src/vim.h b/src/vim.h
index 4b41857..df396ec 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2154,8 +2154,9 @@
 # define number_width(x) 7
 #endif
 
-/* This must come after including proto.h */
-#if !(defined(FEAT_MBYTE) && defined(WIN3264))
+/* This must come after including proto.h.
+ * For VMS this is defined in macros.h. */
+#if !(defined(FEAT_MBYTE) && defined(WIN3264)) && !defined(VMS)
 # define mch_open(n, m, p)	open((n), (m), (p))
 # define mch_fopen(n, p)	fopen((n), (p))
 #endif