[LegacyPassManager] Deprecate the BasicBlockPass/Manager.

Summary:
The BasicBlockManager is potentially broken and should not be used.
Replace all uses of the BasicBlockPass with a FunctionBlockPass+loop on
blocks.

Reviewers: chandlerc

Subscribers: jholewinski, sanjoy.google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68234

llvm-svn: 373254