patch 8.0.1745: build failure on MS-Windows

Problem:    Build failure on MS-Windows.
Solution:   Build job arguments for MS-Windows. Fix allocating job twice.
diff --git a/src/structs.h b/src/structs.h
index 55dd1fe..8f35a73 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1488,7 +1488,7 @@
     int		jv_copyID;
 
     channel_T	*jv_channel;	/* channel for I/O, reference counted */
-    char_u	**argv;		/* command line used to start the job */
+    char_u	**jv_argv;	/* command line used to start the job */
 };
 
 /*