[BFI][CGP] Add limited support for detecting missed BFI updates and fix one in CodeGenPrepare.

Summary:
This helps detect some missed BFI updates during CodeGenPrepare.

This is debug build only and disabled behind a flag.

Fix a missed update in CodeGenPrepare::dupRetToEnableTailCallOpts().

Reviewers: davidxl

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77417