Linux doesn't have this, but since I do truncate(2) in the kernel, it would
be more consistent to do it 'at'-style. (I will remove truncate(2) from the
kernel and let libc call truncateat(2) soon anyway).
These functions were non-standard and their use compared to the execv*
family is questionable. Additionally, they would have to repeat much of
the code from the execl* family of functions. In the end, they were removed
because they weren't strictly needed and less bloat is better here. Besides
programs that would use these functions would need to ship their own
versions to be portable.