Minimum CMake version required to build.

It seems like there are a sizable number of issues being created where people can't successfully compile the C++ code due to old CMake (#2076, #2001, #2045 ).
#2076 and #2001 are due to cmake forwarding unknown compiler flags to nvcc, and #2045 because a required CMake module (FindPython3) is only available on CMake 3.12+.
#2076 is fixed, accoding to the author, by upgrading to CMake 3.13.2 so I would expect #2001 to also be fixed with that version.

However 3.13 seems like a fairly high version requirement for the project, as that is beyond the current Ubuntu LTS default CMake (which is 3.10), even though CMake itself is quite easy to upgrade (prebuilt binaries are available on their website, and packages are also available on pip and conda).

I have WIP backport of the FindPython3 module and with that I manage to successfully compile torchvision with CMake 3.10 - I can't personally reproduce the errors in #2076 and #2001.

My idea is then to land the FindPython3 Module backport and require the minimum CMake version to be 3.10, and to tell people that experience nvcc-related build failures to upgrade their version to at least 3.13.
@fmassa what do you think?

Start by reviewing the proposed FindPython3 module backport and the CMake-related failures in issues #2076, #2001, and #2045. Verify whether the project builds with CMake 3.10, determine the minimum version needed for nvcc-related failures, and document the resulting requirements.