cat: catch 2nd+ splice's error

[oech3]

needed for non-backported version for cat/splice.sh.

$ strace -o /dev/null -e inject=splice:error=EINTR:when=3 target/debug/cat /dev/zero
cat: /dev/zero: Interrupted system call

Closes #12832 (remove also drain_pipe)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/tail-n0f (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/misc/write-errors was skipped on 'main' but is now failing.