patch 9.0.1381: ACCESS_ names have a conflict with on some systems

Problem:    ACCESS_ names have a conflict with on some systems.
Solution:   Rename by prepending VIM_. (Ola Söder, closes #12105)
diff --git a/src/structs.h b/src/structs.h
index 46a71cb..39248a7 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1469,9 +1469,9 @@
 #define TTFLAG_SUPER	    0x40    // object from "super".
 
 typedef enum {
-    ACCESS_PRIVATE,	// read/write only inside th class
-    ACCESS_READ,	// read everywhere, write only inside th class
-    ACCESS_ALL		// read/write everywhere
+    VIM_ACCESS_PRIVATE,	// read/write only inside th class
+    VIM_ACCESS_READ,	// read everywhere, write only inside th class
+    VIM_ACCESS_ALL	// read/write everywhere
 } omacc_T;
 
 /*