gui: Update header docs for IGraphicBufferConsumer/Producer/BufferQueue

Also fix compiler warnings for libgui

Change-Id: I0ee38d9ad5eaa82d55bf812d291da8c433581cef
diff --git a/libs/gui/IGraphicBufferConsumer.cpp b/libs/gui/IGraphicBufferConsumer.cpp
index 9574b61..876c895 100644
--- a/libs/gui/IGraphicBufferConsumer.cpp
+++ b/libs/gui/IGraphicBufferConsumer.cpp
@@ -223,7 +223,7 @@
     }
 
     virtual status_t releaseBuffer(int buf, uint64_t frameNumber,
-            EGLDisplay display, EGLSyncKHR fence,
+            EGLDisplay display __attribute__((unused)), EGLSyncKHR fence __attribute__((unused)),
             const sp<Fence>& releaseFence) {
         Parcel data, reply;
         data.writeInterfaceToken(IGraphicBufferConsumer::getInterfaceDescriptor());