Work around a kernel bug on Android.

runtime/vm/signal_handler.h

Index: runtime/vm/signal_handler.h
diff --git a/runtime/vm/signal_handler.h b/runtime/vm/signal_handler.h
index b204c55d55f1b127f781fc8c73b8c50989861b3d..376ef78f17f13c20c95f090fc22fc50f141dd85b 100644
--- a/runtime/vm/signal_handler.h
+++ b/runtime/vm/signal_handler.h
@@ -43,6 +43,9 @@ typedef void (*SignalAction)(int signal, siginfo_t* info,
 
 class SignalHandler : public AllStatic {
  public:
+  // Note: older linux kernels on ARM might require a trampoline to
+  // work around incorrect Thumb -> ARM transitions. See SignalHandlerTrampoline
+  // in thread_interrupter_android.cc for more details.
   static void Install(SignalAction action);
   static void Remove();
   static uintptr_t GetProgramCounter(const mcontext_t& mcontext);