Frameworks/base: Wall Werror in core/jni

Turn on -Wall -Werror in core/jni. Fix warnings.

Clang TODO: For GCC we need to turn off Wunused-but-set-variable in
the GL bindings. However, Clang doesn't have that warning and thus
complains about an unknown pragma. It is necessary to make the
pragma #ifdef-ed on the compiler being GCC.

Change-Id: I14cab48d45c2771eef0432082356c47ed44a3d7f
diff --git a/core/jni/android_view_SurfaceControl.cpp b/core/jni/android_view_SurfaceControl.cpp
index 06c22ae..adfcdb0 100644
--- a/core/jni/android_view_SurfaceControl.cpp
+++ b/core/jni/android_view_SurfaceControl.cpp
@@ -134,7 +134,7 @@
     status_t res;
     if (allLayers) {
         minLayer = 0;
-        maxLayer = -1UL;
+        maxLayer = -1;
     }
 
     res = screenshot->update(displayToken, sourceCrop, width, height,