[fpc-pascal] Win64 SEH patch fixes some Firebird embedded bugs

[Reinier Olislagers]

Just compiled FPC with -dTEST_WIN64_SEH and noticed that fixes bugs
17360 Firebird database exceptions don't generate EIBDatabaseError but a
general exception on 64 bit windows
21581: Firebird embedded x64 Windows: CreateDB fails with an exception

It may well also remove the need for the nasty workaround applied in bug
19116: RunError(32) when reading BLOB with IBConnection on Win64
... which might also be interesting given Marco's remark:
> * While reading up on the previous issue I saw warnings that getting the blob size this way might be notoriously slow. 

Thought I'd let everybody know in case they run into Firebird x64
(embedded) problems on Windows and to indicate that implementing the SEH
patch might be a good idea...

Thanks,
Reinier