Reduce warnings noise when including wtf/Platform.h in KJS

[Stephen Kelly]

Stephen Kelly wrote:

>> These are defined with "1" if acceptable and undefined if the feature is
>> not present.
> 
> This is the problem that should be fixed.
> 
> It should be 0 if the feature is not present. Please fix that instead.

Hmm, or maybe your fix is ok. 

I don't know where the values come from, but there seems to be a code smell 
somewhere...

Thanks,

Steve.