Don't manually mess with sigaltstack on Android any more.

Bionic now takes care of things.

Bug: 8557703
Change-Id: I0510a193f2433eaf54c9c6ac3415c85b50a7f1d2
diff --git a/runtime/thread.h b/runtime/thread.h
index 0daf763..e496cfc 100644
--- a/runtime/thread.h
+++ b/runtime/thread.h
@@ -618,6 +618,9 @@
   void InitPthreadKeySelf();
   void InitStackHwm();
 
+  void SetUpAlternateSignalStack();
+  void TearDownAlternateSignalStack();
+
   void NotifyLocked(Thread* self) EXCLUSIVE_LOCKS_REQUIRED(wait_mutex_);
 
   static void ThreadExitCallback(void* arg);