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/runtime/base/stringpiece.h b/runtime/base/stringpiece.h
index b8de308..d793bb6 100644
--- a/runtime/base/stringpiece.h
+++ b/runtime/base/stringpiece.h
@@ -67,8 +67,8 @@
     ptr_ = nullptr;
     length_ = 0;
   }
-  void set(const char* data, size_type len) {
-    ptr_ = data;
+  void set(const char* data_in, size_type len) {
+    ptr_ = data_in;
     length_ = len;
   }
   void set(const char* str) {
@@ -79,8 +79,8 @@
       length_ = 0;
     }
   }
-  void set(const void* data, size_type len) {
-    ptr_ = reinterpret_cast<const char*>(data);
+  void set(const void* data_in, size_type len) {
+    ptr_ = reinterpret_cast<const char*>(data_in);
     length_ = len;
   }