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_.
diff --git a/src/syntax.c b/src/syntax.c
index 9c17a58..f01c840 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -4809,7 +4809,7 @@
      * 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 == '$' || mch_isFullName(eap->arg))
     {