JNI libraries in CtsVerifier should use libstdc++ STL

Android Build system uses libc++ by default if LOCAL_CXX_STL is
undefined. However, Android N introduced b/28250179, which prevents
the 3rd party apps from linking to libc++ in the system partition.

Bug: 30399537
Change-Id: I980f150df1675c3054546d89a1197626b53949c1
(cherry picked from commit a34c8745e16837f9ab20be1248d2a8bdcda77786)
diff --git a/apps/CtsVerifier/jni/verifier/Android.mk b/apps/CtsVerifier/jni/verifier/Android.mk
index 4840e62..2978b06 100644
--- a/apps/CtsVerifier/jni/verifier/Android.mk
+++ b/apps/CtsVerifier/jni/verifier/Android.mk
@@ -32,4 +32,6 @@
 
 LOCAL_SHARED_LIBRARIES := liblog
 
+LOCAL_CXX_STL := libstdc++
+
 include $(BUILD_SHARED_LIBRARY)