[PATCH] Bitcode: Add bitcode format compatibility test

[Vedant Kumar]

> Absolutely. The primary thing I can think of that could slip through this approach easily are changes that only have a manifestation at the bitcode level, not in IR. E.g. how operand indices in the bitcode were changed from absolute indices in the function to being relative to the instruction's position. Maybe also add BitCodeFormat.rst to your list of files to diff?

I've added this to my checklist.

I wanted to send a ping out on this, since Hans is planning on doing RC2 soon. It'd be nice to have this before the final release candidate.

IIRC David was concerned about duplicate tests -- I can work on cleaning that up.

vedant