[PATCH] Add renameat2 function [BZ #17662]

[Paul Eggert]

Florian Weimer wrote:
> as Joseph pointed out, there is a different emulation strategy with a different 
> failure mode (use link and potentially leave behind a hard-linked file under 
> both names).

So far I haven't run into applications that prefer that strategy, i.e., nobody 
seems using that strategy on older kernels that don't support renameat2 with 
RENAME_NOREPLACE. If we run into enough apps that prefer this fallback, we could 
add a flag for it of course.