vim-patch:8.1.1667: flags for Ex commands may clash with other symbols

Problem:    Flags for Ex commands may clash with other symbols.
Solution:   Prepend with EX_.
8071cb2c64

N/A patches for version.c:

vim-patch:8.1.1672: "make cmdidxs" doesn't work

Problem:    "make cmdidxs" doesn't work.
Solution:   Update macro names. (Naruhiko Nishino, closes vim/vim#4660)
d94ac0caca

Error message for src/nvim/ex_cmds.lua
which omits the "EX_" prefix for the flags.

src/nvim/syntax.c

@@ -4275,7 +4275,7 @@ static void syn_cmd_include(exarg_T *eap, int syncing)
    * Everything that's left, up to the next command, should be the
    * filename to include.
    */
-  eap->argt |= (XFILE | NOSPC);
+  eap->argt |= (EX_XFILE | EX_NOSPC);
   separate_nextcmd(eap);
   if (*eap->arg == '<' || *eap->arg == '$' || path_is_absolute(eap->arg)) {
     // For an absolute path, "$VIM/..." or "<sfile>.." we ":source" the