[fpc-pascal] INVALID_SOCKET constant not defined for Linux

[LacaK]

> Under *nix socket calls are just general runtime calls, and they use the
> same convention and constants for errorhandling as all other calls.
As I know "nothing" about Linux, then it is safe to check?:
   socket := Sockets.FPSocket(...);
   if socket = -1 then // invalid socket returned due to error ...

This technique is used in fcl-net which should be cross-platform.
So I am right, when I say that also in Linux invald socket = -1
(in other words: in case of error syscall() returns always -1)

Becuase in other place I see another test "if socket < 0 then ..."
(which may mean that any negative value can be returned)

L.