Compatibility layer to transition from UniquePtr to std::unique_ptr.

Use ART_WITH_STLPORT (enabled for the target) to cause the use of UniquePtr,
for the host switch to std::unique_ptr. For now the type remains called
UniquePtr.
Make dalvik compile with clang on the host, move its build to C++11.

Change-Id: I5ba8d2757904bc089ed62047ea03de3c0853fb12
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index d855eee..20a66d4 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -52,7 +52,7 @@
 #include "runtime.h"
 #include "scoped_thread_state_change.h"
 #include "handle_scope-inl.h"
-#include "UniquePtr.h"
+#include "UniquePtrCompat.h"
 #include "utils.h"
 
 using ::art::mirror::ArtField;