Add locking to atomic operations in rw/rcu tests

Add locking to atomic operations in rw/rcu tests

I neglected to add locks to the calls to CRYPTO_atomic_add in these
test, which on newer compilers is fine, as atomic operations are
defined.  However on older compilers the __ATOMIC_ACQ_REL definition is
missing causing these function to be implemented using an rwlock, which
when NULL causes the locks to fail.

Fix this my creating the lock and using them appropriately

Fixes #24000

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/24001)