Support CUDA 10.2

[japm48]

While compiling with CUDA 10.2 I get the following error:
error: cannot find libdevice for sm_52. Provide path to different CUDA installation via --cuda-path, or pass -nocudalib to build without linking with libdevice.

Apparently the problem is that CudaStringToVersion returns CudaVersion::UNKNOWN.

Unless I'm missing anything, the addition of CudaVersion::CUDA_102 after wherever CUDA_101 is found should be trivial. Of course, with PtxFeature = "+ptx64", as PTX 6.5 can wait.

[kkwli]

https://reviews.llvm.org/D74571

[japm48]

Well, for the record I managed to make it work without recompiling clang, with a very hackish solution.

In case this is useful to someone:

• Edit .../cuda/version.txt to mock CUDA version 10.1.105.
• Comment out #error "Unsupported CUDA version!" in __clang_cuda_runtime_wrapper.h.

Feel free to close the issue now or wait until 10.2 (with ptx65, etc.) is properly supported.