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
0e2da18081