[BOLT] Use continuous output addresses in delta encoding in BAT
Make output function addresses be delta-encoded wrt last offset in the
previous function. This reduces the deltas in function start addresses.
Test Plan:
Reduces BAT section size to:
- large binary: 12218860 bytes (0.32x original),
- medium binary: 1606580 bytes (0.27x original),
- small binary: 404 bytes (0.28x original),
Reviewers: rafaelauler
Reviewed By: rafaelauler
Pull Request: https://github.com/llvm/llvm-project/pull/76904