shred,sort,split: fix ftruncate error reporting

shred,sort,split: fix ftruncate error reporting

Problem reported for split by Scott Worley (Bug#33761):
* src/shred.c (do_wipefd):
Also report an error if ftruncate fails	on a shared memory object.
* src/sort.c (get_outstatus): New function.
(stream_open, avoid_trashing_input): Use it.
* src/sort.c (stream_open):
* src/split.c (create):
If ftruncate fails, do not report an error
unless it is a regular file or a shared memory object.