headers: time.h: Add back _TIMEZONE_DEFINED

Some downstream projects depend on it to avoid multiple definition of
struct timezone.

Signed-off-by: Zhongteng Gui <dragon-archer@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>

mingw-w64-headers/crt/time.h

diff --git a/mingw-w64-headers/crt/time.h b/mingw-w64-headers/crt/time.h
index 3d69e7c..17df578 100644
--- a/mingw-w64-headers/crt/time.h
+++ b/mingw-w64-headers/crt/time.h
@@ -163,10 +163,13 @@
 
 #include <_timeval.h>
 
+#ifndef _TIMEZONE_DEFINED
+#define _TIMEZONE_DEFINED /* Compatibility only, as some downstream projects use it */
 struct timezone {
   int tz_minuteswest;
   int tz_dsttime;
 };
+#endif
 
 int __cdecl mingw_gettimeofday(struct timeval* _Tv, struct timezone* _Tz);