This does 2 things for us:
1. Allows us to compile-time depend on any features from new headers,
instead of having to conditionally compile based on Windows SDK version.
2. Allows us to reference d3d12.h when compiling for non-Windows.
Reviewed-by: Bill Kristiansen <billkris@microsoft.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7937>
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