added extra fs link and fixed execute_program warning

cmake/helpers.cmake

@@ -0,0 +1,46 @@
+function(default_build_type val)
+if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+  message(STATUS "No build type selected, default to Release")
+  set(CMAKE_BUILD_TYPE ${val} CACHE STRING "Build type (default ${val})" FORCE)
+endif()
+endfunction()
+
+function(set_std_fs_lib)
+# from pybind11
+# Check if we need to add -lstdc++fs or -lc++fs or nothing
+if(DEFINED CMAKE_CXX_STANDARD AND CMAKE_CXX_STANDARD LESS 17)
+  set(STD_FS_NO_LIB_NEEDED TRUE)
+elseif(MSVC)
+  set(STD_FS_NO_LIB_NEEDED TRUE)
+else()
+  file(
+    WRITE ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    "#include <filesystem>\nint main(int argc, char ** argv) {\n  std::filesystem::path p(argv[0]);\n  return p.string().length();\n}"
+  )
+  try_compile(
+    STD_FS_NO_LIB_NEEDED ${CMAKE_CURRENT_BINARY_DIR}
+    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    COMPILE_DEFINITIONS -std=c++17)
+  try_compile(
+    STD_FS_NEEDS_STDCXXFS ${CMAKE_CURRENT_BINARY_DIR}
+    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    COMPILE_DEFINITIONS -std=c++17
+    LINK_LIBRARIES stdc++fs)
+  try_compile(
+    STD_FS_NEEDS_CXXFS ${CMAKE_CURRENT_BINARY_DIR}
+    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    COMPILE_DEFINITIONS -std=c++17
+    LINK_LIBRARIES c++fs)
+endif()
+
+if(${STD_FS_NEEDS_STDCXXFS})
+  set(STD_FS_LIB stdc++fs PARENT_SCOPE)
+elseif(${STD_FS_NEEDS_CXXFS})
+  set(STD_FS_LIB c++fs PARENT_SCOPE)
+elseif(${STD_FS_NO_LIB_NEEDED})
+  set(STD_FS_LIB "" PARENT_SCOPE)
+else()
+  message(WARNING "Unknown C++17 compiler - not passing -lstdc++fs")
+  set(STD_FS_LIB "")
+endif()
+endfunction()