Fix up the makefiles and some samples.

Add LOCAL_DEX_PREOPT := false to force the samples to build actual apks.

In addition, fix a couple of other small issues:

- TtsEngine didn't have the api level set properly.
- SimpleJNI used a non-ndk library and was using libc++.

Change-Id: I1fd7c187956eed4620049bb746f4d62babcd648a
diff --git a/samples/SupportAppNavigation/Android.mk b/samples/SupportAppNavigation/Android.mk
index 6a30e1f..b832911 100644
--- a/samples/SupportAppNavigation/Android.mk
+++ b/samples/SupportAppNavigation/Android.mk
@@ -11,6 +11,8 @@
 
 LOCAL_SDK_VERSION := current
 
+LOCAL_DEX_PREOPT := false
+
 include $(BUILD_PACKAGE)
 
 LOCAL_PROGUARD_FLAG_FILES := proguard.flags