fix building by owc12: GetLongPathName() is available since Win2K only

src/os/win32/ngx_win32_config.h

diff --git a/src/os/win32/ngx_win32_config.h b/src/os/win32/ngx_win32_config.h
index 0dcba98..f098eae 100644
--- a/src/os/win32/ngx_win32_config.h
+++ b/src/os/win32/ngx_win32_config.h
@@ -9,7 +9,7 @@
 
 
 #define WIN32         0x0400
-#define _WIN32_WINNT  0x0400
+#define _WIN32_WINNT  0x0500
 
 
 #define STRICT