Set back CUDA default to C++14.

CMakeLists.txt

@@ -260,9 +260,6 @@ endif()
 set(CMAKE_CXX_STANDARD ${QMC_CXX_STANDARD})
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
-set(CMAKE_CUDA_STANDARD ${QMC_CXX_STANDARD})
-set(CMAKE_CUDA_STANDARD_REQUIRED TRUE)
-set(CMAKE_CUDA_EXTENSIONS OFF)
 
 # Check that a C++ compiler is compatible with the underlying libstdc++
 include(Testlibstdc++)
@@ -672,6 +669,12 @@ if(QMC_CUDA OR ENABLE_CUDA)
       unset(CUDA_ARCH CACHE)
       message(FATAL_ERROR "CUDA_ARCH option has been removed. Use -DCMAKE_CUDA_ARCHITECTURES=80 if -DCUDA_ARCH=sm_80 was used.")
     endif()
+    # a few production machines use CUDA 10 which only supports C++14.
+    if(NOT DEFINED CMAKE_CUDA_STANDARD)
+      set(CMAKE_CUDA_STANDARD 14)
+    endif()
+    set(CMAKE_CUDA_STANDARD_REQUIRED TRUE)
+    set(CMAKE_CUDA_EXTENSIONS OFF)
     if(NOT DEFINED CMAKE_CUDA_ARCHITECTURES)
       set(CMAKE_CUDA_ARCHITECTURES 70)
     endif()