[RFC] Make _FILE_OFFSET_BITS=64 default.

[Joseph S. Myers]

There's another problem with using such an assertion in fts.h: it's not 
the correct condition for the two ABIs to be the same.  On MIPS n64, 
struct stat and struct stat64 have different layout and so 
_FILE_OFFSET_BITS=64 is an ABI change despite __off_t and __off64_t having 
the same size (and part of the public fts interface is a pointer to struct 
stat).

-- 
Joseph S. Myers
joseph@codesourcery.com