* include/cygwin/time.h: Switch to timezone variable by default. Add

comment.

winsup/cygwin/include/cygwin/time.h

@@ -29,7 +29,9 @@ time_t __cdecl timegm (struct tm *);
 #   define daylight _daylight
 # endif
 
-# ifndef timezonevar
+/* The timezone function is only kept for backward compatibility.
+   POSIX expects the timezone variable as XSI extension. */
+# ifdef __timezonefunc__
 char __cdecl *timezone (void);
 # elif !defined(timezone)
 #   define timezone _timezone