[clang] [clang][codegen] Add a verifier IR pass before any further passes. (PR #68015)

[John McCall via cfe-commits]

rjmccall wrote:

Thank you.  If your PR is just changing things so that we run the existing verifier on the direct result of IR generation instead of only verifying it after a few passes run, I agree that it's the right thing to do.

https://github.com/llvm/llvm-project/pull/68015