[RFC] Make _FILE_OFFSET_BITS=64 default.

[Joseph S. Myers]

On Thu, 13 Mar 2014, Rich Felker wrote:

> If this happens to work, it's purely by chance/redundancy. -U
> overrides all -D for the same identifier, even subsequent ones.

We can presume glibc is built with the "gcc" driver, not any separate 
"c99" driver with different precedence rules (see GCC bug 40960).

-- 
Joseph S. Myers
joseph@codesourcery.com