Bug#835940: nvidia-cuda-toolkit: non-standard gcc/g++ used for build (gcc-5)

[lumin]

Hello guys,

I successfully compiled caffe with CUDA_8.0.44-2 and
clang-3.8 (the current default clang). Maybe we can
replace GCC-5 with Clang-3.8 to solve this problem.

That means Stretch still has chance to ship CUDA8,
and users are expected to compile with Clang/LLVM
instead of GCC-6, as long as the CUDA rDepends
compile with clang.

I only tested caffe-contrib.