Fix multithreaded backtraces for seccomp processes.

Add threads to the existing seccomp backtrace test to prevent
regressing this.

Bug: http://b/114139908
Bug: http://b/115349586
Test: debuggerd_test32
Test: debuggerd_test64
Change-Id: I07fbe1619b60f0008deb045a249f9045404478c2
diff --git a/debuggerd/handler/fallback.h b/debuggerd/handler/fallback.h
new file mode 100644
index 0000000..597f582
--- /dev/null
+++ b/debuggerd/handler/fallback.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+static void* const kDebuggerdFallbackSivalPtrRequestDump = reinterpret_cast<void*>(~0UL);
+static const uintptr_t kDebuggerdFallbackSivalUintptrRequestDump = ~0UL;