Build errors(warnings) on macOS

[Jinming-Hu]

In file included from /Users/jamis/Desktop/azure-sdk-for-cpp/sdk/core/azure-core/src/http/curl/curl.cpp:15:
In file included from /Users/jamis/Desktop/azure-sdk-for-cpp/sdk/core/azure-core/inc/azure/core/http/curl_transport.hpp:11:
/Users/jamis/Desktop/azure-sdk-for-cpp/sdk/core/azure-core/inc/azure/core/context.hpp:156:14: error: definition of implicit copy constructor for 'Context' is deprecated because it has a user-declared copy assignment operator [-Werror,-Wdeprecated-copy]
    Context& operator=(const Context& other) = default;
             ^
/Users/jamis/Desktop/azure-sdk-for-cpp/sdk/core/azure-core/inc/azure/core/context.hpp:167:14: note: in implicit copy constructor for 'Azure::Core::Context' first required here
      return Context{std::make_shared<ContextSharedState>(m_contextSharedState, deadline)};
             ^
1 error generated.
make[2]: *** [sdk/core/azure-core/CMakeFiles/azure-core.dir/src/http/curl/curl.cpp.o] Error 1
make[1]: *** [sdk/core/azure-core/CMakeFiles/azure-core.dir/all] Error 2
make: *** [all] Error 2