Enable emission of debugger-friendly bitcode

- Add "-g" flag to llvm-rs-cc in order to emit debug metadata
- Add optimization level parameter -O and tests
- Add lit based tests (use llvm-lit from libbcc/tests/debuginfo)
-- Add README file for lit-tests directory

Change-Id: I5e2f6f9b6f536fa7a10de008b54ac0878cf352a9
19 files changed