Add a libFollySegFault.so convenience lib

Summary:
As per glibc's `libSegFault.so`, provide a standalone DSO that
non-fbcode binaries can `LD_PRELOAD` to get symbolification
via folly's symbolizer on signals/crashes.

Reviewed By: mzlee

Differential Revision: D52861325

fbshipit-source-id: f26329a431ae1abeb0aba208c2d3fce6a84b080a

folly/experimental/symbolizer/tool/LibSegFault.cpp

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * 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.
+ */
+
+#include <folly/experimental/symbolizer/SignalHandler.h>
+
+static void __attribute__((constructor)) install_handler(void) {
+  folly::symbolizer::installFatalSignalHandler();
+}

folly/experimental/symbolizer/tool/libFollySegFault.so.v

@@ -0,0 +1,4 @@
+{
+  /* We don't export anything, since our constructor does all the work. */
+  local: *;
+};