Free Pascal has several Pascal syntax modes: FPC, TurboPascal, Object Free Pascal, Delphi and Mac Pascal (whatever it is). Maybe something else I forgot to mention. Objective-C maybe. In Object Free Pascal mode generics are incompatible with Delphi because apparently Free Pascal developers invented their own syntax for generics; however in Delphi syntax mode Free Pascal generics syntax conforms to Delphi generics syntax (more or less). While Free Pascal might not support latest additions to generics introduced in Delphi, it should be able to compile simplier cases; so in general it should be possible to compile same source code with generics both in FreePascal and Delphi.
Most likely, Free Pascal does not support generic constraints: this TIntfListGenericType<T: IInterfaceList> thing