(VERSION): Provide default definition, like etags.c

does, because Windows build can't snarf this from version.el.

lib-src/ebrowse.c

@@ -3477,6 +3477,10 @@ usage (error)
 /* Display version and copyright info.  The VERSION macro is set
    from the Makefile and contains the Emacs version.  */
 
+#ifndef VERSION
+# define VERSION "21"
+#endif
+
 void
 version ()
 {