Explicitly link libstdc++.a for static gtest executables.

Change-Id: I29e3a4036264acd00dfa3229c9d0fc52ee20830e
diff --git a/core/target_test_internal.mk b/core/target_test_internal.mk
index e531356..7b99678 100644
--- a/core/target_test_internal.mk
+++ b/core/target_test_internal.mk
@@ -12,6 +12,7 @@
                     bionic/libstdc++/include \
                     external/stlport/stlport
 LOCAL_SHARED_LIBRARIES += libstlport
+LOCAL_STATIC_LIBRARIES += libstdc++
 endif
 
 ifndef LOCAL_MODULE_PATH