[fpc-pascal] Blockread and buffers

[Peter Vreman]

> I don't know, whether other compiler modes support const and out. If
> yes, the RTL/FCL/LCL functions should use it. This do mean e.g.

For compatibility we can't do this. Delphi also doesn't warn. And making
the warning dependent on the compiler mode will make things too complex.
Because it then dependents on the compiler mode used to compile a used
unit that contains a function and not on the compiler mode used in the
current unit.