Cuda < 9 compilation fix suggested by Chris Sullivan (#1853)

* Cuda < 9 compilation fix suggested by Chris Sullivan.

* Reworked conditional cuda compilation to support more compiler variants.

* Tweak to allow CUDA compilation with CUDA 8 & gcc 5.4

* Explicitly check for clang if not gcc.

* Removed extraneous comment

src/ngraph/runtime/gpu/CMakeLists.txt

@@ -72,8 +72,38 @@ if (NGRAPH_GPU_ENABLE)
 	    -gencode=arch=compute_70,code=compute_70)
     endif()
 
-    set_source_files_properties( ${CUDA_SRC} PROPERTIES CUDA_SOURCE_PROPERTY_FORMAT OBJ)
-    cuda_compile(CUDA_OBJ ${CUDA_SRC} STATIC)
+    set (DO_CUDA_COMPILE FALSE)
+    if (CUDA9_FOUND)
+        if (("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU"))
+            # CUDA 9 supports up to gcc 6.x
+            if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.0)
+                set (DO_CUDA_COMPILE TRUE)
+            endif()
+        elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+            # CUDA 9 supports up to clang 3.9
+            if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.0)
+                set (DO_CUDA_COMPILE TRUE)
+            endif()
+        endif()
+    else()
+        # CUDA 8 (minimum version of CUDA we support)
+        if (("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU"))
+            # Current release of CUDA 8 supports up to gcc 5.4
+            if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.5)
+                set (DO_CUDA_COMPILE TRUE)
+            endif()
+        elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+            # CUDA 8 supports up to clang 3.8
+            if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.9)
+                set (DO_CUDA_COMPILE TRUE)
+            endif()
+        endif()
+    endif()
+
+    if (DO_CUDA_COMPILE)
+        set_source_files_properties( ${CUDA_SRC} PROPERTIES CUDA_SOURCE_PROPERTY_FORMAT OBJ)
+        cuda_compile(CUDA_OBJ ${CUDA_SRC} STATIC)
+    endif()
 
     add_library(gpu_backend SHARED ${SRC} ${CUDA_OBJ})
     set_target_properties(gpu_backend PROPERTIES VERSION ${NGRAPH_VERSION} SOVERSION ${NGRAPH_API_VERSION})