CrossVcl is a set of tools for Delphi developers, which can create VCL applications for macOS and Linux with Embarcadero Delphi.
CrossVcl not an emulator, it is WinAPI implementation for other platform.
CrossVcl covers only UI side of WinAPI (except DirectX) requred by VCL. For non-UI part of application you should use cross-platform routines from RTL and other frameworks.
All thrid-party tools should be modified (at least changing shared library names from for example "user32.dll" to CrossVclLib). It depends on tools, some of them can be used with simple modification, other requires more.
All new Embarcadero Delphi compiler based on LLVM technology and called "nextgen" compiler. Nextgen compilers don't have support of AnsiString, ShortString, embedded asseembler code and use ARC model for all objects.