Add the _Unwind_Complete symbol, with an empty method.

This method is defined by the ARM EHABI to exist as a chance to run
any cleanup needed at the end of exception handling. We don't need
to do anything in it at this time, but we should export the symbol
to be compliant.

Change-Id: I99c2e739cc4a343fa631252406080f22a8598f36
Merge pull request #111 from awong-dev/complete

Add the _Unwind_Complete symbol, with an empty method.