osutil.c: use readdir instead of readdir64
Some systems (e.g. *BSD) don't have a readdir64 function - the regular
readdir already uses 64-bit types.
On other systems (Linux, Solaris, ...), if Python was compiled with large
file support, Python.h will define _LARGEFILE_SOURCE and _FILE_OFFSET_BITS=64,
so that any call to readdir will actually be a call to readdir64. If Python
was not compiled with large file support, we probably don't want to define
these macros to avoid ABI problems.
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Ran 20 tests in 0.000s
OK