[CUDA] Added rudimentary support for CUDA-9 and sm_70.

For now CUDA-9 is not included in the list of CUDA versions clang
searches for, so the path to CUDA-9 must be explicitly passed
via --cuda-path=.

On LLVM side NVPTX added sm_70 GPU type which bumps required
PTX version to 6.0, but otherwise is equivalent to sm_62 at the moment.

Differential Revision: https://reviews.llvm.org/D37576

llvm-svn: 312734
diff --git a/clang/lib/Basic/Targets/NVPTX.cpp b/clang/lib/Basic/Targets/NVPTX.cpp
index 92e21c3..3889f09 100644
--- a/clang/lib/Basic/Targets/NVPTX.cpp
+++ b/clang/lib/Basic/Targets/NVPTX.cpp
@@ -183,6 +183,8 @@
         return "610";
       case CudaArch::SM_62:
         return "620";
+      case CudaArch::SM_70:
+        return "700";
       }
       llvm_unreachable("unhandled CudaArch");
     }();