Hide internal __old_readdir64 function to allow direct access within
libc.so and libc.a without using GOT nor PLT.
[BZ #18822]
* sysdeps/unix/sysv/linux/i386/olddirent.h (__old_readdir64):
Add libc_hidden_proto.
* sysdeps/unix/sysv/linux/i386/readdir64.c (__old_readdir64):
Add libc_hidden_def.