libc: Fix _obstack_newchunk public symbol vis

975bca165c3e10e74c05c0384fd58f45a7025a3c avoided relocations to
_obstack_newchunk used by obstack_vprintf but missed to enable the
corresponding public symbol which is used by the obstack macros.

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/misc/gnu/obstack.c

@@ -322,9 +322,7 @@ _obstack_newchunk (struct obstack *h, int length)
   /* The new chunk certainly contains no empty object yet.  */
   h->maybe_empty_object = 0;
 }
-# if 0
-libc_hidden_def (_obstack_newchunk)
-# endif
+libc_hidden_def(_obstack_newchunk)
 
 /* Return nonzero if object OBJ has been allocated from obstack H.
    This is here for debugging.