executor: avoid setsid() errors

See commit bc144f9.  The justification
applies to other BSDs as well, so apply the same workaround.

executor/common_bsd.h

@@ -396,7 +396,7 @@ static void sandbox_common()
 #if SYZ_EXECUTOR
 	if (!flag_threaded)
 #endif
-		if (setsid() == -1)
+		if (setsid() == -1 && errno != EPERM)
 			fail("setsid failed");
 #endif