[clang] [Clang] Add codegen option to add passbuilder callback functions (PR #70171)

[William Moses via cfe-commits]

wsmoses wrote:

@efriedma-quic I've removed the non-options stuff, please review it at your convenience.

Let me see if I can make the other stuff work in a different way.

https://github.com/llvm/llvm-project/pull/70171