Merge pull request microsoft#693 from ChuckM2/feature/chuckm/DX12

D3D12LinkedGpus sample build fix.

Fix d3dx12.h readme formatting

Fix d3dx12.h readme formatting

Fix d3dx12.h readme formatting

Fix d3dx12.h readme formatting

Merge pull request microsoft#683 from robbiesri/microsoftgh-652-mesh-…

…shaders-buildbuild

Fix compile-time errors in D3D12MeshShaders samples (error C2102: '&' requires l-value)

Merge pull request microsoft#676 from sherief/master

Fixed the DXR samples so they can run on (I'm wheezing) Surface Book 3.

Merge pull request microsoft#673 from gongminmin/RemoveEmpty

Remove nonsense vertexData.empty() calls

Merge pull request microsoft#673 from gongminmin/RemoveEmpty

Remove nonsense vertexData.empty() calls

Merge pull request microsoft#671 from microsoft/UpdateDX12UltimateSam…

…pleLinks

Update readme for DX12U samples