print warning if compiling pytorch ops with torch 1.7 and cuda 11

[benjaminum]

Adds a warning if we compile the pytorch ops with torch 1.7 or later and cuda 11.
See #3324

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This change is 

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[stotko]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @benjaminum)

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3rdparty/CMake/FindPytorch.cmake, line 65 at r1 (raw file):

        set_target_properties( torch_cpu PROPERTIES INTERFACE_COMPILE_OPTIONS "" )

        if( CUDA_VERSION VERSION_GREATER_EQUAL "11.0" AND

CUDAToolkit_VERSION instead of old deprecated CUDA_VERSION. The respective find_package(CUDAToolkit REQUIRED) call is already performed above, so the former is safely defined while the later is not.

[stotko]

Reviewed 1 of 1 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @benjaminum)

[benjaminum]

Changes have been included in #3049