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/nth_caller_visitor.h b/runtime/nth_caller_visitor.h
index 374a80e..a851f21 100644
--- a/runtime/nth_caller_visitor.h
+++ b/runtime/nth_caller_visitor.h
@@ -26,9 +26,9 @@
 
 // Walks up the stack 'n' callers, when used with Thread::WalkStack.
 struct NthCallerVisitor : public StackVisitor {
-  NthCallerVisitor(Thread* thread, size_t n, bool include_runtime_and_upcalls = false)
-      : StackVisitor(thread, NULL), n(n), include_runtime_and_upcalls_(include_runtime_and_upcalls),
-        count(0), caller(NULL) {}
+  NthCallerVisitor(Thread* thread, size_t n_in, bool include_runtime_and_upcalls = false)
+      : StackVisitor(thread, NULL), n(n_in),
+        include_runtime_and_upcalls_(include_runtime_and_upcalls), count(0), caller(NULL) {}
 
   bool VisitFrame() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     mirror::ArtMethod* m = GetMethod();