tools/lib/lockdep: Fix the build on recent kernels

The following upstream commit:

  4a389810 ("kernel/locking/lockdep.c: convert hash tables to hlists")

broke the tools/lib/lockdep build. Add trivial RCU wrappers to fix it.

These wrappers should probably be moved into their own header file.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Krinkin <krinkin.m.u@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>