libgui: Enable -Weverything and -Werror

Enables -Weverything and -Werror, with just a few exceptions for
warnings we can't (or shouldn't need to) work around.

Change-Id: I034abec27bf4020d84af60d7acc1939c59986dd6
diff --git a/libs/gui/StreamSplitter.cpp b/libs/gui/StreamSplitter.cpp
index 25e6cab..8146869 100644
--- a/libs/gui/StreamSplitter.cpp
+++ b/libs/gui/StreamSplitter.cpp
@@ -141,7 +141,7 @@
 
     IGraphicBufferProducer::QueueBufferInput queueInput(
             bufferItem.mTimestamp, bufferItem.mIsAutoTimestamp,
-            bufferItem.mCrop, bufferItem.mScalingMode,
+            bufferItem.mCrop, static_cast<int32_t>(bufferItem.mScalingMode),
             bufferItem.mTransform, bufferItem.mIsDroppable,
             bufferItem.mFence);