add dirent.h support

[Christian Haake]

Hey,
configuring the newlib (1.20.0) for target=arm-elf lacks directory traversing (dirent.h) support as is generally known.
On making our embedded OS kind of POSIX compliant meanwhile we have a fat file system. For some projects (like e.g. bash) to compile successfully at least dirent.h must be available.
What would be your approach to add directory traversing support? First I guess I have to disable the #error pragma in sys/dirent.h, haven't I ?!?
Thanks in advance...
Chris