Force cxx 17

cmake/modules/CMakeListsExternal.cmake

@@ -58,7 +58,8 @@ if(NOT DEFINED NICAFEMTO_SUBDIR_BUILD)
         If(NOT _HAS_CXX17_FLAG)
       Message(FATAL_ERROR "The used C++ compiler (${CMAKE_CXX_COMPILER}) does not support C++17. NicaFemto can only be compiled with compilers supporting C++11. Please install such an compiler.")
       else()
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")      
+        set(CMAKE_CXX_STANDARD 17)
+#set(CMAKE_CXX_STANDARD_REQUIRED ON)     
     EndIf()