Example of x64 contracts with STL support are available in tests/stl_tests/test_contracts directory. CMake files for gcc version 7 and clang 10 STL support are located in scripts directory. For gcc version 8 and version 9 STL scripts should be modified accordingly.
Compiling with AppleClang
AppleClang requires to define custom allocator in collections, so you have to instantiate string, vector and map with explicit custom allocator:
// `stl_allocator` is defined in x86-64/contracts/libstd/stl_allocator.hpp
// Instead of std::string str;
std_string str;// From x86-64/contracts/libstd/stl_string.hpp