Use default cpp fmt build script.

vendor/Fmt/test/cuda-test/CMakeLists.txt

@@ -0,0 +1,73 @@
+# We can find some usecases which follow the guide of CMake which uses
+# `enable_language(CUDA)` instead of `find_package(CUDA)` and let the CMake
+# built-in functions use NVCC.
+
+# See: https://cmake.org/cmake/help/latest/module/FindCUDA.html#replacement
+#
+# However, this requires CMake version 3.10 or higher and we can't be sure most
+# of the CUDA projects are using those.
+#
+# This test relies on `find_package(CUDA)` in the parent CMake config.
+
+# These can be updated when NVCC becomes ready for C++ 17 features
+# https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#cpp14-language-features
+set(CMAKE_CUDA_STANDARD 14)
+set(CMAKE_CUDA_STANDARD_REQUIRED 14)
+
+# In this test, we assume that the user is going to compile CUDA source code
+# with some libraries (fmt in this case).
+#
+# In addition to that, this test invokes both the C++ host compiler and NVCC
+# by providing another (non-CUDA) C++ source code.
+if (${CMAKE_VERSION} VERSION_LESS 3.15)
+  # https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/index.html
+  list(APPEND CUDA_NVCC_FLAGS "-std=c++14")
+  if (MSVC)
+    # This is the solution of pytorch:
+    # https://github.com/pytorch/pytorch/pull/7118
+    list(APPEND CUDA_NVCC_FLAGS "-Xcompiler" "/std:c++14")
+    list(APPEND CUDA_NVCC_FLAGS "-Xcompiler" "/Zc:__cplusplus")
+    # for the reason of this -Xcompiler options, see below.
+  endif ()
+  cuda_add_executable(fmt-in-cuda-test cuda-cpp14.cu cpp14.cc)
+  target_compile_features(fmt-in-cuda-test PRIVATE cxx_std_14)
+  if (MSVC)
+    # This part is for (non-CUDA) C++ code. MSVC can define incorrect
+    # `__cplusplus` macro. Fix for the issue is to use additional compiler flag. 
+    #
+    # See Also:
+    # https://devblogs.microsoft.com/cppblog/msvc-now-correctly-reports-__cplusplus/
+    # https://github.com/Microsoft/vscode-cpptools/issues/2595
+    target_compile_options(fmt-in-cuda-test PRIVATE /Zc:__cplusplus /permissive-)
+  endif ()
+else()
+  # now using a "new" way of handling CUDA
+  add_executable(fmt-in-cuda-test cuda-cpp14.cu cpp14.cc)
+  set_target_properties(fmt-in-cuda-test PROPERTIES CUDA_SEPARABLE_COMPILATION ON)
+  target_compile_features(fmt-in-cuda-test PRIVATE cxx_std_14)
+  if (MSVC)
+    # with MSVC, 'cxx_std_14' will only propagate to the host code (MSVC), but will
+    # not set __cplusplus correctly anyway, while nvcc will ignore it.
+    # If specified for nvcc on the command line as '-std=c++14' nvcc will emit this
+    # message instead:
+    # nvcc warning : The -std=c++14 flag is not supported with the configured host
+    #                compiler. Flag will be ignored.
+    set_property(SOURCE cuda-cpp14.cu APPEND PROPERTY
+      COMPILE_OPTIONS -Xcompiler /std:c++14 -Xcompiler /Zc:__cplusplus)
+    set_property(SOURCE cpp14.cc APPEND PROPERTY
+      COMPILE_OPTIONS /std:c++14 /Zc:__cplusplus)
+  endif()
+endif()
+
+get_target_property(IN_USE_CUDA_STANDARD fmt-in-cuda-test CUDA_STANDARD)
+message(STATUS "cuda_standard:          ${IN_USE_CUDA_STANDARD}")
+
+get_target_property(IN_USE_CUDA_STANDARD_REQUIRED
+    fmt-in-cuda-test CUDA_STANDARD_REQUIRED)
+message(STATUS "cuda_standard_required: ${IN_USE_CUDA_STANDARD_REQUIRED}")
+
+# We don't use PUBLIC or other keyword for reasons explained in the
+# CUDA_LINK_LIBRARIES_KEYWORD section in
+# https://cmake.org/cmake/help/latest/module/FindCUDA.html
+target_link_libraries(fmt-in-cuda-test fmt::fmt)
+

vendor/Fmt/test/cuda-test/cpp14.cc

@@ -0,0 +1,11 @@
+#include <fmt/core.h>
+
+// The purpose of this part is to ensure NVCC's host compiler also supports
+// the standard version. See 'cuda-cpp14.cu'.
+//
+// https://en.cppreference.com/w/cpp/preprocessor/replace#Predefined_macros
+static_assert(__cplusplus >= 201402L, "expect C++ 2014 for host compiler");
+
+auto make_message_cpp() -> std::string {
+  return fmt::format("host compiler \t: __cplusplus == {}", __cplusplus);
+}

vendor/Fmt/test/cuda-test/cuda-cpp14.cu

@@ -0,0 +1,28 @@
+//  Direct NVCC command line example:
+//
+//  nvcc ./cuda-cpp14.cu -x cu -I"../include" -l"fmtd" -L"../build/Debug" \
+//       -std=c++14 -Xcompiler /std:c++14 -Xcompiler /Zc:__cplusplus
+
+// Ensure that we are using the latest C++ standard for NVCC
+// The version is C++14
+//
+// https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#c-cplusplus-language-support
+// https://en.cppreference.com/w/cpp/preprocessor/replace#Predefined_macros
+static_assert(__cplusplus >= 201402L, "expect C++ 2014 for nvcc");
+
+#include <fmt/core.h>
+
+#include <cuda.h>
+#include <iostream>
+
+extern auto make_message_cpp() -> std::string;
+extern auto make_message_cuda() -> std::string;
+
+int main() {
+  std::cout << make_message_cuda() << std::endl;
+  std::cout << make_message_cpp() << std::endl;
+}
+
+auto make_message_cuda() -> std::string {
+  return fmt::format("nvcc compiler \t: __cplusplus == {}", __cplusplus);
+}