perror() changes the orientation of stderr to byte-oriented mode if stderr is not oriented yet.

[Andreas Köpke]

Hi folks, thanks for the great work. 

I'm working on bare metal using newlib - with the changes to perror it does 
not compile anymore: none of the headers (sys/uio.h, unistd.h) are known.

So I guess we need some split here.

Thanks, Andreas