cmake build system (#1314)

* Changed c api to compile under MSVC

* Include functional.h header for MSVC

* Add cmake build

src/data/sparse_batch_page.h

@@ -23,6 +23,10 @@
 #include <thread>
 #endif
 
+#ifdef _MSC_VER
+#include <functional>
+#endif
+
 namespace xgboost {
 namespace data {
 /*!