selftests/bpf: tests with delayed read/precision makrs in loop body

These test cases try to hide read and precision marks from loop
convergence logic: marks would only be assigned on subsequent loop
iterations or after exploring states pushed to env->head stack first.
Without verifier fix to use exact states comparison logic for
iterators convergence these tests (except 'triple_continue') would be
errorneously marked as safe.

Signed-off-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: eddyz87