* Changes for Mingw64 compilation to ensure long is a consistent size.
Mainly impacts the Java API which would not compile, but there may be
silent errors on Windows with large datasets before this patch (as long
is 32-bits when compiled with mingw64 even in 64-bit mode).
* Adding ifdefs to ensure it still compiles on MacOS
* Makefile and create_jni.bat changes for Windows.
* Switching XGDMatrixCreateFromCSREx JNI call to use size_t cast
* Fixing lint error, adding profile switching to jvm-packages build to make create-jni.bat get called, adding myself to Contributors.Md
