Preparation for transition to libc++.

Move the dependency on libc++ to its own makefile so that we can switch in a
single place between libc++ and stlport.

Change-Id: Ie61e7d054dcd049e36d5e7298c27d8a4abe6edf7
diff --git a/dalvikvm/dalvikvm.cc b/dalvikvm/dalvikvm.cc
index 3486c1d..8d71a7c 100644
--- a/dalvikvm/dalvikvm.cc
+++ b/dalvikvm/dalvikvm.cc
@@ -15,11 +15,10 @@
  */
 
 #include <signal.h>
+#include <stdio.h>
+#include <string.h>
 
 #include <algorithm>
-#include <cstdio>
-#include <cstring>
-#include <string>
 
 #include "jni.h"
 #include "JniInvocation.h"