Compiling the tests with -Wextra results to lots of warnings for unused
parameters. Annotate these cases with the `unused' attribute to avoid
the warnings.
(consume_some_stack_space): New function.
(main): Call consume_some_stack_space() before establishing the
rlimit. Otherwise, stack-expansion may bump into
the address-space rlimit.
(Logical change 1.290)