vim-patch:8.1.2233: cannot get the Vim command line arguments (#12117)

Problem:    Cannot get the Vim command line arguments.
Solution:   Add v:argv. (Dmitri Vereshchagin, closes vim/vim#1322)
69bf634858

src/nvim/eval.h

@@ -159,6 +159,7 @@ typedef enum {
     VV_ECHOSPACE,
     VV_EXITING,
     VV_LUA,
+    VV_ARGV,
 } VimVarIndex;
 
 /// All recognized msgpack types