Move libcore to C++11.

Change-Id: I1942be8f7cef51265d53272f36a217e88bfede94
diff --git a/NativeCode.mk b/NativeCode.mk
index 3a22575..52ab6d7 100644
--- a/NativeCode.mk
+++ b/NativeCode.mk
@@ -68,6 +68,7 @@
 core_static_libraries := $(LOCAL_STATIC_LIBRARIES)
 core_cflags := -Wall -Wextra -Werror
 core_cflags += -DJNI_JARJAR_PREFIX="com/android/"
+core_cppflags += -std=gnu++11
 
 core_test_files := \
   luni/src/test/native/test_openssl_engine.cpp \