Hello Everyone,
I found a somewhat working solution. As suggested in the error message, I specified -mByproduct std_xyz' to disable this diagnostic.
I added the following lines
list(APPEND core_implicit_modules "-mByproduct" "std_vector")
list(APPEND core_implicit_modules "-mByproduct" "std_functional")
list(APPEND core_implicit_modules "-mByproduct" "std_sstream")
list(APPEND core_implicit_modules "-mByproduct" "std_numeric")
list(APPEND core_implicit_modules "-mByproduct" "std_fstream")
list(APPEND core_implicit_modules "-mByproduct" "std_iostream")
list(APPEND core_implicit_modules "-mByproduct" "std_map")
list(APPEND core_implicit_modules "-mByproduct" "std_unordered_set")
list(APPEND core_implicit_modules "-mByproduct" "std_chrono")
list(APPEND core_implicit_modules "-mByproduct" "std_complex")
list(APPEND core_implicit_modules "-mByproduct" "std_forward_list")
list(APPEND core_implicit_modules "-mByproduct" "std_list")
list(APPEND core_implicit_modules "-mByproduct" "std_condition_variable")
list(APPEND core_implicit_modules "-mByproduct" "std_thread")
list(APPEND core_implicit_modules "-mByproduct" "std_queue")
manually after the following lines in core/CMakeLists.txt and rebuilt ROOT. It worked for me.
list(APPEND core_implicit_modules "-m" "_Builtin_intrinsics" "-mByproduct" "_Builtin_intrinsics")
list(APPEND core_implicit_modules "-mByproduct" "ROOT_Foundation_Stage1_NoRTTI")
list(APPEND core_implicit_modules "-mByproduct" "ROOT_Foundation_C")
list(APPEND core_implicit_modules "-mByproduct" "ROOT_Rtypes")