This compile flag was required previously when Bitcoin Core was using C++11, and libmultiprocess headers needed to be compiled with C++14 in order to be compatible with newer versions of Cap'n Proto. The flag was updated to C++17 since then.
But now Bitcoin Core has been updated to use C++20 and having the C++17 flag causes errors when the std::u8string type is referenced in bitcoin code. So just remove the C++ flag and let the application be responsible for choosing the C++ version.
This compile flag was required previously when Bitcoin Core was using C++11,
and libmultiprocess headers needed to be compiled with C++14 in order to be
compatible with newer versions of Cap'n Proto. The flag was updated to C++17
since then.
But now Bitcoin Core has been updated to use C++20 and having the C++17 flag
causes errors when the std::u8string type is referenced in bitcoin code. So
just remove the C++ flag and let the application be responsible for choosing
the C++ version.