[fpc-pascal] Dependencies of FPC_HAS_FEATURE_XXX

[Sven Barth]

Hello again!

I found the next ones: the threading feature depends on exceptions 
(InitStdExceptions) and I/O (InitStdIO) (both not easy to implement). 
Also it uses CheckInitialStkLength. The declaration of this function is 
enclosed by FPC_HAS_FEATURE_STACKCHECK, so the call should be enclosed, too.

I really consider this dependencies as a bug... but I'll wait for your 
opinions (at least some days :P ).

Hmm... if this speeds things up: shall I enclose the problematic places 
with ifdefs and send a patch along with the bug report?

Regards,
Sven