Because the file is not available on all platforms the inclusion comes
after the user options in order to disable including it. But that means
the inclusion also follows after the defined scanner states, which are
generated as simple #defines to numbers. If the included unistd.h e.g.
uses variables in function definitions with the same names this could
result in compilation errors.
Interactive mode has to be disabled too as it relies on isatty() from
unistd.h. Since we don't use the scanners interactively, this is not a
problem and might even make the scanners a bit faster.
Fixes#2806.
97c4551ec8