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/jni/jni_compiler_test.cc b/compiler/jni/jni_compiler_test.cc
index 1132046..2755442 100644
--- a/compiler/jni/jni_compiler_test.cc
+++ b/compiler/jni/jni_compiler_test.cc
@@ -785,9 +785,9 @@
     EXPECT_EQ(11, trace_array->GetLength());
 
     // Check stack trace entries have expected values
-    for (int32_t i = 0; i < trace_array->GetLength(); ++i) {
-      EXPECT_EQ(-2, trace_array->Get(i)->GetLineNumber());
-      mirror::StackTraceElement* ste = trace_array->Get(i);
+    for (int32_t j = 0; j < trace_array->GetLength(); ++j) {
+      EXPECT_EQ(-2, trace_array->Get(j)->GetLineNumber());
+      mirror::StackTraceElement* ste = trace_array->Get(j);
       EXPECT_STREQ("MyClassNatives.java", ste->GetFileName()->ToModifiedUtf8().c_str());
       EXPECT_STREQ("MyClassNatives", ste->GetDeclaringClass()->ToModifiedUtf8().c_str());
       EXPECT_STREQ("fooI", ste->GetMethodName()->ToModifiedUtf8().c_str());