ART: Move JNI files to runtime/jni/ .

Test: Rely on TreeHugger.
Change-Id: I9cae11191ef1567ae9453be498882a7767285140
diff --git a/runtime/native/java_lang_System.cc b/runtime/native/java_lang_System.cc
index 390f026..2c4184c 100644
--- a/runtime/native/java_lang_System.cc
+++ b/runtime/native/java_lang_System.cc
@@ -20,7 +20,7 @@
 
 #include "common_throws.h"
 #include "gc/accounting/card_table-inl.h"
-#include "jni_internal.h"
+#include "jni/jni_internal.h"
 #include "mirror/array.h"
 #include "mirror/class-inl.h"
 #include "mirror/class.h"