Integrating Protobuf into Unreal Engine 4 (Linux)

Question

I'm having trouble integrating protobuf (3.20.4) into UE4 as a static library and packaging for linux.

The packaging fails with these errors :

undefined symbol: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::resize(unsigned long, char)
Error        PackagingResults     undefined symbol: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::reserve(unsigned long)
Error        PackagingResults     undefined symbol: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_append(char const*, unsigned long)

I'm assuming it's because I compiled them against libstdc++ rather than libc++ but I can't work out how to compile them using cmake with libc++.