gui: Update header docs for IGraphicBufferConsumer/Producer/BufferQueue

Also fix compiler warnings for libgui

Change-Id: I0ee38d9ad5eaa82d55bf812d291da8c433581cef
diff --git a/libs/gui/BufferQueue.cpp b/libs/gui/BufferQueue.cpp
index c43f29e..a95ac64 100644
--- a/libs/gui/BufferQueue.cpp
+++ b/libs/gui/BufferQueue.cpp
@@ -703,7 +703,7 @@
     return err;
 }
 
-void BufferQueue::binderDied(const wp<IBinder>& who) {
+void BufferQueue::binderDied(const wp<IBinder>& who __attribute__((unused))) {
     // If we're here, it means that a producer we were connected to died.
     // We're GUARANTEED that we still are connected to it because it has no other way
     // to get disconnected -- or -- we wouldn't be here because we're removing this