Switch ndk_test from gnustl_static to c++_static

gnustl_static is no longer supported.
diff --git a/ndk_test/jni/Application.mk b/ndk_test/jni/Application.mk
index d7ccd34..4e66465 100644
--- a/ndk_test/jni/Application.mk
+++ b/ndk_test/jni/Application.mk
@@ -1,5 +1,5 @@
 APP_ABI := all
 APP_BUILD_SCRIPT := Android.mk
-APP_STL := gnustl_static
+APP_STL := c++_static
 APP_PLATFORM := android-9
 NDK_TOOLCHAIN_VERSION := 4.9