selftests: vDSO: skip getrandom test if architecture is unsupported

If the getrandom test compiles for an arch, don't exit fatally if the
actual cpu it's running on is unsupported.
Suggested-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tools/testing/selftests/vDSO/vdso_test_getrandom.c

@@ -104,6 +104,7 @@ static void vgetrandom_init(void)
 	const char *version = versions[VDSO_VERSION];
 	const char *name = names[VDSO_NAMES][6];
 	unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
+	size_t ret;
 
 	if (!sysinfo_ehdr) {
 		printf("AT_SYSINFO_EHDR is not present!\n");
@@ -115,7 +116,11 @@ static void vgetrandom_init(void)
 		printf("%s is missing!\n", name);
 		exit(KSFT_FAIL);
 	}
-	if (vgrnd.fn(NULL, 0, 0, &vgrnd.params, ~0UL) != 0) {
+	ret = vgrnd.fn(NULL, 0, 0, &vgrnd.params, ~0UL);
+	if (ret == -ENOSYS) {
+		printf("unsupported architecture\n");
+		exit(KSFT_SKIP);
+	} else if (ret) {
 		printf("failed to fetch vgetrandom params!\n");
 		exit(KSFT_FAIL);
 	}