[fpc-pascal] Why is cthreads unit not included by default

[Marco van de Voort]

In our previous episode, Henry Vermaak said:
> 2009/8/27 Michael Van Canneyt <michael at freepascal.org>:
> >
> > Because I want a FPC program to depend only on the Linux kernel, not on the
> > C library.
> >
> > There are FPC programs from 8 years back that still work with the current
> > kernel. Try that with a program that depends on the C library.
> 
> The only reason for this is the fact that the rtl is compiled into fpc
> executables.  If fpc had an rtl as a lib (like c), we would be in the
> same boat.

More or less. But FPC's rtl doesn't pretend to be an OS interface.

That's also why e.g. Windows suffers less from this. Library linking issues
are more isolated and the API is very static. (stuff is added, but not
changed)