selftests/bpf: add CO-RE relocs modifiers/typedef tests

Add tests validating correct handling of various combinations of
typedefs and const/volatile/restrict modifiers.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>