Bug#873405: Please update to llvm-toolchain 4.0 or, better, 5.0

[Lumin]

Control: clone -1 -2
Control: reassign -2 nvidia-cuda-toolkit 8.0.44-4
Control: retitle -2 cuda: moving away from clang-3.8 to gcc-6 ?
Control: severity -2 important

Hi,

The CUDA toolkit will not be ready for Clang-4.0 . As claimed by Nvidia,
the highest version that CUDA 9.0 (will be released soon) supports
is Clang-3.9 . Since the Clang maintainer would like to remove
Clang-3.8 and Clang-3.9, the cuda package cannot depend on
them anymore.

The current version (CUDA 8.0.44) supports GCC (<= 5) and
Clang (<= 3.8). GCC-5 is still available in the archive.
We can unblock the ROM of clang-3.8 by temporarily by
switching back to GCC-5 but that will block the ROM of
GCC-5 in the future.

CUDA 9.0.103 (release-candidate) supports GCC-6
and Clang-3.9 . Clang-3.9 is now suffering from the GCC-7
headers as shown at bottom. GCC-6 works with CUDA 9 compiling
the examples provided by upstream, although some CUDA
applications seems not ready for CUDA 9.0 .

So if doko is about to also keep GCC-6 in the archive for a long time,
we should switch the compiler to GCC-6 for the CUDA 9.0 upload.

-------------------------------------------------

❯❯❯ nvcc -ccbin clang++-3.9 matrixMul.cu -I../../common/inc
                                   Mon 28 Aug 2017 04:36:32 AM UTC
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/bits/std_abs.h(101):
error: identifier "__float128" is undefined

/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/bits/std_abs.h(102):
error: identifier "__float128" is undefined

2 errors detected in the compilation of
"/tmp/tmpxft_00002c27_00000000-8_matrixMul.cpp1.ii".

❯❯❯ nvcc -ccbin clang++-4.0 matrixMul.cu -I../../common/inc
                           439ms  Mon 28 Aug 2017 04:36:34 AM UTC
nvcc fatal   : The version ('40001') of the host compiler ('clang') is
not supported

❯❯❯ nvcc --version
                                   Mon 28 Aug 2017 04:47:22 AM UTC
nvcc: NVIDIA (R) Cuda compiler driver
Copyright (c) 2005-2017 NVIDIA Corporation
Built on Mon_Jun_26_16:13:28_CDT_2017
Cuda compilation tools, release 9.0, V9.0.102

-- 
Best,
Lumin