You can add your own functions which do conversion when Delphi is used, but just return the string as is when FPC is used, via conditional compilation. They do the required thing within them, and just use them consistently instead of Delphi specific functions. Define them in a shared unit. I do this for different platforms. I don't use Delphi, but I have seen other code which does something similar in order to support both Delphi and FPC.
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