selftests: vDSO: fix vDSO name for powerpc

Following error occurs when running vdso_test_correctness on powerpc:

~ # ./vdso_test_correctness
[WARN]	failed to find vDSO
[SKIP]	No vDSO, so skipping clock_gettime() tests
[SKIP]	No vDSO, so skipping clock_gettime64() tests
[RUN]	Testing getcpu...
[OK]	CPU 0: syscall: cpu 0, node 0

On powerpc, vDSO is neither called linux-vdso.so.1 nor linux-gate.so.1
but linux-vdso32.so.1 or linux-vdso64.so.1.

Also search those two names before giving up.

Fixes: c7e5789b ("kselftest: Move test_vdso to the vDSO test suite")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tools/testing/selftests/vDSO/vdso_test_correctness.c

@@ -114,6 +114,12 @@ static void fill_function_pointers()
 	if (!vdso)
 		vdso = dlopen("linux-gate.so.1",
 			      RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
+	if (!vdso)
+		vdso = dlopen("linux-vdso32.so.1",
+			      RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
+	if (!vdso)
+		vdso = dlopen("linux-vdso64.so.1",
+			      RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
 	if (!vdso) {
 		printf("[WARN]\tfailed to find vDSO\n");
 		return;