Enable Modules on Windows

ROOT has several features that interact with libraries and require implicit header inclusion. This can be triggered by reading or writing data on disk, or user actions at the prompt. Exposing the full shared library descriptors to the interpreter at runtime translates into an increased memory footprint. ROOT’s exploratory programming concepts allow implicit and explicit runtime shared library loading. It requires the interpreter to load the library descriptor. Re-parsing of descriptors’ content has a noticeable effect on runtime performance. C++ Modules are designed to minimize the reparsing of the same header content by providing an efficient on-disk representation of the C++ Code. C++ Modules have been implemented for Unix and OS X systems already and it is expected that with next release of ROOT, C++ modules will be default on OS X. This project aims to extend the C++ Modules support for Windows, by implementing compatible solutions to the UNIX baseline and also display corresponding performance results.