bpf, tests: Add tests for ALU operations implemented with function calls

32-bit JITs may implement complex ALU64 instructions using function calls.
The new tests check aspects related to this, such as register clobbering
and register argument re-ordering.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210809091829.810076-9-johan.almbladh@anyfinetworks.com