[llvm] [clang] [PassBuilder] Add a mechanism for adding passbuilder callbacks for static builds (PR #70171)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

The new option in CodeGenOptions.h seems fine.

If your goal is to statically inject passes into the clang executable, I don't understand why the existing LLVM plugin infrastructure isn't sufficient for your needs.  You mention "modifying Extension.def", but that file is generated by the build system based on the plugins found by CMake.

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