Prepare for improving Windows networking compatibility. (#8234)

* Prepare for improving Windows networking compatibility.

* Include dmlc filesystem indirectly as dmlc/filesystem.h includes windows.h, which
  conflicts with winsock2.h
* Define `NOMINMAX` conditionally.
* Link the winsock library when mysys32 is used.
* Add config file for read the doc.

tests/cpp/data/test_data.cc

@@ -2,13 +2,14 @@
  * Copyright 2019-2022 by XGBoost Contributors
  */
 #include <gtest/gtest.h>
-#include <dmlc/filesystem.h>
+
 #include <fstream>
 #include <memory>
 #include <vector>
 
-#include "xgboost/data.h"
+#include "../filesystem.h"  // dmlc::TemporaryDirectory
 #include "../helpers.h"
+#include "xgboost/data.h"
 
 namespace xgboost {
 TEST(SparsePage, PushCSC) {