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/compiled_method.h b/compiler/compiled_method.h
index cdae8d2..0361cd1 100644
--- a/compiler/compiled_method.h
+++ b/compiler/compiled_method.h
@@ -162,7 +162,7 @@
       }
       this->resize(i + 1);
 
-      for (size_t i = size(); --i >= 1; ) {
+      for (i = size(); --i >= 1; ) {
         (*this)[i].from_ -= (*this)[i-1].from_;
         (*this)[i].to_ -= (*this)[i-1].to_;
       }