If it isn't imported from a library why would it be in the Import and Export tables?
Only those with export modifier or in the exports section are put into the Export table and only those with external <LIBRARY> or external <LIBRARY> name <FUNC> are part of the Import table (and the suggestion by marcov is external name <FUNC> which has a small, but in this case significant different meaning due to the missing library name).
I have no doubt you know the internals of the FPC compiler better than I do, therefore, I will take your word for it. The presence of the keyword "external" gave me the impression that it could end up in the exports and imports tables. Your point that without the keyword "exports" that doesn't happen makes sense.
ETA:On the other hand, doesn't it end up creating symbols for each alias in the DWARF/Stabs debugging symbol tables ?