Migrate the kasan_rcu_uaf test to the KUnit framework.

Changes to the implementation of the test:

- Call rcu_barrier() after call_rcu() to make that the RCU callbacks get
  triggered before the test is over.

- Cast pointer passed to rcu_dereference_protected as __rcu to get rid of
  the Sparse warning.

- Check that KASAN prints a report via KUNIT_EXPECT_KASAN_FAIL.

Initially, this test was intended to check that Generic KASAN prints
auxiliary stack traces for RCU objects. Nevertheless, the test is enabled
for all modes to make that KASAN reports bad accesses in RCU callbacks.

The presence of auxiliary stack traces for the Generic mode needs to be
inspected manually.

Link: https://lkml.kernel.org/r/897ee08d6cd0ba7e8a4fbfd9d8502823a2f922e6.1664298455.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>