add more PHONY declarations

Queue-based interfaces are able to spread the syscall overhead across
multiple requests.
Add a new io_uring variant submitting 10 read requests with a single
io_uring_enter call.

Adapt bench.c and all other variants to support variable numbers of
read requests issued by do_read(...).

Work work work

See merge request i4/manycore/fgbs-syscall-eval!4

Work work work

See merge request i4/manycore/fgbs-syscall-eval!3

work work work

See merge request i4/manycore/fgbs-syscall-eval!2

I don't know how this breaks but stopping the watch in the signal handler
overflows when summing up the clock differences.