CUDA: Add support for the C++14 standard flag.

CUDA 9 toolkit has announced support for C++14 flag, so lets allow users
to use it.

Modules/Compiler/NVIDIA-CUDA.cmake

@@ -24,4 +24,10 @@ else()
   set(CMAKE_CUDA98_EXTENSION_COMPILE_OPTION "")
   set(CMAKE_CUDA11_STANDARD_COMPILE_OPTION "-std=c++11")
   set(CMAKE_CUDA11_EXTENSION_COMPILE_OPTION "-std=c++11")
+
+  if (NOT CMAKE_CUDA_COMPILER_VERSION VERSION_LESS 9.0)
+    set(CMAKE_CUDA14_STANDARD_COMPILE_OPTION "-std=c++14")
+    set(CMAKE_CUDA14_EXTENSION_COMPILE_OPTION "-std=c++14")
+  endif()
+
 endif()

Source/cmLocalGenerator.cxx

@@ -1518,6 +1518,7 @@ void cmLocalGenerator::AddCompilerRequirementFlag(
     langStdMap["C"].push_back("99");
     langStdMap["C"].push_back("90");
 
+    langStdMap["CUDA"].push_back("14");
     langStdMap["CUDA"].push_back("11");
     langStdMap["CUDA"].push_back("98");
   }