selftests/rseq: Add rseq syscall errors test

This test adds coverage of expected errors during rseq registration and
unregistration, it disables glibc integration and will thus always
exercise the rseq syscall explictly.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250121213402.1754762-1-mjeanson@efficios.com