[Bitcode][Asm] Teach LLVM to read and write operand bundles.

Summary:
This also adds the first set of tests for operand bundles.

The optimizer has not been audited to ensure that it does the right
thing with operand bundles.

Depends on D12456.

Reviewers: reames, chandlerc, majnemer, dexonsmith, kmod, JosephTremoulet, rnk, bogner

Subscribers: maksfb, llvm-commits

Differential Revision: http://reviews.llvm.org/D12457

llvm-svn: 248551