Initial "compilable" version of mesa/gfxstream on Windows. For now it is
achieved through "#if !DETECT_OS_WINDOWS" directives hence it is NOT
functional. The compilation works with mingw only and the compilation is
tested in a windows host. This commit is intended to only pass the
compilation process without errors.
Also created stub code for a future windows implementation.
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32795>