Overall, this commit is an attempt at merging changes for ezpc from internal repo.

More specifically, some of these changes include:
- Added extern function support to ezpc.
- Added SecureNN as backend to ezpc.
- More bug fixes.
- All test_suite examples' precompiled-output are updated with new compiler changes.
- Added an updated and more complex sample compiled test file in ABY_example.

Tests done
- "make runtest" works fine for all test_suite examples.
- Sample code in ABY_example is also tested to be working with latest ABY.