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_sparse_page_dmatrix.cu

@@ -1,10 +1,10 @@
 // Copyright by Contributors
 
-#include <dmlc/filesystem.h>
-#include "../helpers.h"
 #include "../../../src/common/compressed_iterator.h"
 #include "../../../src/data/ellpack_page.cuh"
 #include "../../../src/data/sparse_page_dmatrix.h"
+#include "../filesystem.h"  // dmlc::TemporaryDirectory
+#include "../helpers.h"
 
 namespace xgboost {