ART: More warnings

Enable -Wno-conversion-null, -Wredundant-decls and -Wshadow in general,
and -Wunused-but-set-parameter for GCC builds.

Change-Id: I81bbdd762213444673c65d85edae594a523836e5
diff --git a/compiler/utils/array_ref.h b/compiler/utils/array_ref.h
index c137e46..1a7f2e8 100644
--- a/compiler/utils/array_ref.h
+++ b/compiler/utils/array_ref.h
@@ -73,8 +73,8 @@
     : array_(array), size_(size) {
   }
 
-  constexpr ArrayRef(T* array, size_t size)
-      : array_(array), size_(size) {
+  constexpr ArrayRef(T* array_in, size_t size_in)
+      : array_(array_in), size_(size_in) {
   }
 
   template <typename Alloc>