fix building --without-http-cache, broken in r2953
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 16a027a..add5b21 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -318,10 +318,14 @@
       ngx_http_upstream_response_length_variable, 0,
       NGX_HTTP_VAR_NOHASH|NGX_HTTP_VAR_NOCACHEABLE, 0 },
 
+#if (NGX_HTTP_CACHE)
+
     { ngx_string("upstream_cache_status"), NULL,
       ngx_http_upstream_cache_status, 0,
       NGX_HTTP_VAR_NOHASH|NGX_HTTP_VAR_NOCACHEABLE, 0 },
 
+#endif
+
     { ngx_null_string, NULL, NULL, 0, 0, 0 }
 };