rseq/selftests: Fix MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ build error under other arch.

Except arch x86, the function rseq_offset_deref_addv is not defined.
The function test_membarrier_manager_thread call rseq_offset_deref_addv
produces a build error.

The RSEQ_ARCH_HAS_OFFSET_DEREF_ADD should contain all the code
for the MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ.
If the other Arch implements this feature,
defined RSEQ_ARCH_HAS_OFFSET_DEREF_ADD in the header file
to ensure that this feature is available.

Following build errors:

param_test.c: In function ‘test_membarrier_worker_thread’:
param_test.c:1164:10: warning: implicit declaration of function ‘rseq_offset_deref_addv’
ret = rseq_offset_deref_addv(&args->percpu_list_ptr,
^~~~~~~~~~~~~~~~~~~~~~
/tmp/ccMj9yHJ.o: In function `test_membarrier_worker_thread':
param_test.c:1164: undefined reference to `rseq_offset_deref_addv'
param_test.c:1164: undefined reference to `rseq_offset_deref_addv'
collect2: error: ld returned 1 exit status
make: *** [/selftests/rseq/param_test_benchmark] Error 1

Signed-off-by: Xingxing Su <[e-mail]>
Acked-by: Mathieu Desnoyers <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/rseq/param_test.c

···
 	return ret;
 }
 
+/* Test MEMBARRIER_CMD_PRIVATE_RESTART_RSEQ_ON_CPU membarrier command. */
+#ifdef RSEQ_ARCH_HAS_OFFSET_DEREF_ADDV
 struct test_membarrier_thread_args {
 	int stop;
 	intptr_t percpu_list_ptr;
···
 	return NULL;
 }
 
-/* Test MEMBARRIER_CMD_PRIVATE_RESTART_RSEQ_ON_CPU membarrier command. */
-#ifdef RSEQ_ARCH_HAS_OFFSET_DEREF_ADDV
 void test_membarrier(void)
 {
 	const int num_threads = opt_threads;