crash_dump: clear the default crash handlers.

crash_dump is a dynamic executable that gets the default crash dumping
handlers set by the linker. Turn them off to prevent crash_dump from
dumping itself.

Bug: http://b/34472671
Test: inserted an abort into crash_dump
Change-Id: Ic9d708805ad47afbb2a9ff37e2ca059f23f421de
diff --git a/debuggerd/crash_dump.cpp b/debuggerd/crash_dump.cpp
index 4db13aa..cd939ef 100644
--- a/debuggerd/crash_dump.cpp
+++ b/debuggerd/crash_dump.cpp
@@ -160,6 +160,12 @@
   return true;
 }
 
+static void signal_handler(int) {
+  // We can't log easily, because the heap might be corrupt.
+  // Just die and let the surrounding log context explain things.
+  _exit(1);
+}
+
 static void abort_handler(pid_t target, const bool& tombstoned_connected,
                           unique_fd& tombstoned_socket, unique_fd& output_fd,
                           const char* abort_msg) {
@@ -175,7 +181,6 @@
 
   dprintf(output_fd.get(), "crash_dump failed to dump process %d: %s\n", target, abort_msg);
 
-  // Don't dump ourselves.
   _exit(1);
 }
 
@@ -201,6 +206,11 @@
     abort_handler(target, tombstoned_connected, tombstoned_socket, output_fd, abort_msg);
   });
 
+  // Don't try to dump ourselves.
+  struct sigaction action = {};
+  action.sa_handler = signal_handler;
+  debuggerd_register_handlers(&action);
+
   if (argc != 2) {
     return 1;
   }