[DCC Error] SynBidirSock.pas(755): E1025 Unsupported language feature: 'Object'

I have figured it out. In Project Options -> Delphi Compiler -> Output - C/C++ menu the setting C/C++ Output File generation DEFAULTS to Generate all C++ Builder files (including package libs) even for a Delphi package....

Change this setting to Generate DCUs only, recompile...  resulting in 0 errors. Hope this helps someone else.