Be explicit about using C++11.

The fact that the build system bumped the default standard for the NDK
is probably not desirable. Be explicit so we can fix that.

Change-Id: I1573ef32d7b9c9d23fb45b1016b6848efd079f43
diff --git a/tests/tests/rscpp/librscpptest/Android.mk b/tests/tests/rscpp/librscpptest/Android.mk
index df8ce29f..0fa6f27 100644
--- a/tests/tests/rscpp/librscpptest/Android.mk
+++ b/tests/tests/rscpp/librscpptest/Android.mk
@@ -45,6 +45,8 @@
 LOCAL_C_INCLUDES += frameworks/rs/cpp
 LOCAL_C_INCLUDES += frameworks/rs
 
+LOCAL_CPPFLAGS := -std=c++11
+
 LOCAL_SHARED_LIBRARIES := libdl liblog
 LOCAL_STATIC_LIBRARIES := libRScpp_static libcutils