title: fail to link cuda example with clang++-9 under Ubuntu 18.04
body: <p>I am trying to follow the example in
  <a href="https://llvm.org/docs/CompileCudaWithLLVM.html#invoking-clang" rel="nofollow noreferrer">https://llvm.org/docs/CompileCudaWithLLVM.html#invoking-clang</a>
  I use Ubuntu 18.04.3 LTS, clang version 9.0.0-2
  The device I have is (snippet from the output of deviceQuery):</p>
  <pre><code>Detected 1 CUDA Capable device(s)
  
  Device 0: &quot;Quadro P520&quot;
    CUDA Driver Version / Runtime Version          10.2 / 10.2
    CUDA Capability Major/Minor version number:    6.1
  </code></pre>
  <p>I ran the command:</p>
  <pre><code>clang++-9 --verbose --cuda-path=/usr/local/cuda-10.2 axpy.cu -o axpy --cuda-gpu-arch=sm_61 -L/usr/local/cuda-10.2 -lcudart_static -ldl -lrt -pthread
  </code></pre>
  <p>And the output is:</p>
  <pre><code>clang version 9.0.0-2~ubuntu18.04.1 (tags/RELEASE_900/final)
  Target: x86_64-pc-linux-gnu
  Thread model: posix
  InstalledDir: /usr/bin
  Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/8
  Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
  Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0
  Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
  Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
  Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
  Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
  Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
  Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0
  Candidate multilib: .;@m64
  Selected multilib: .;@m64
  Found CUDA installation: /usr/local/cuda-10.2, version unknown
  clang: error: cannot find libdevice for sm_61. Provide path to different CUDA installation via --cuda-path, or pass -nocudalib to build without linking with libdevice.
  </code></pre>
  <p>As far as I can tell, libdevice is right where it should be:</p>
  <pre><code>~&gt;ls /usr/local/cuda-10.2/nvvm/libdevice/
  libdevice.10.bc
  </code></pre>
  <p>What am I doing wrong ?</p>
  <p><strong>Added Nov 2020:</strong>
  Following @ArtemB comment, I tried running it with clang++-10, which throws a warning, but compiles and runs just fine.</p>