Fix fxc path for non-Visual Studio builds

[matyalatte]

I found that CMAKE_SYSTEM_VERSION did not have the revision number. This tiny change ensures non-Visual Studio generators (e.g. Ninja) can find fxc without requiring manual environment variable adjustments.

[walbourn]

Thanks for the feedback. I think the safer thing would be to make it:

HINTS "C:/Program Files (x86)/Windows Kits/10/bin/${CMAKE_SYSTEM_VERSION}/${DIRECTX_HOST_ARCH}"
    "C:/Program Files (x86)/Windows Kits/10/bin/${CMAKE_SYSTEM_VERSION}.0/${DIRECTX_HOST_ARCH}"
    "C:/Program Files (x86)/Windows Kits/10/bin/${CMAKE_VS_WINDOWS_TARGET_PLATFORM_VERSION}/${DIRECTX_HOST_ARCH}")

And the same changes should be made in:

https://github.com/microsoft/DirectXTK/blob/main/CMakeLists.txt#L260

https://github.com/microsoft/DirectXTK12/blob/main/CMakeLists.txt#L295
https://github.com/microsoft/DirectXTK12/blob/main/CMakeLists.txt#L300

Would you like to submit PRs for these?