bug#27986: 26.0.50; 'rename-file' can rename files without confirmation

[Paul Eggert]

Ken Brown wrote:
> This is now done.  The implementation will appear in the next Cygwin release.  
> When that release occurs, I'll install something like the attached patch.

Thanks.

> Question: Is the patch OK as is, or should I make the call to renameat2 
> conditional on CYGWIN?  In other words, is it safe to assume that renameat2 is 
> defined on any platform on which RENAME_NOREPLACE is defined but not SYS_renameat2?

It should be OK, for the same reason the RENAME_EXCL branch is OK (it assumes 
renameatx_np). If we run across some future platform where it doesn't work, we 
can port it then. As far as I know, Cygwin will be the first platform with 
renameat2 in its C library.