[llvm-branch-commits] [Clang] Invoke pass plugin preCodeGenCallback (PR #171872)

[Alexis Engelke via llvm-branch-commits]

https://github.com/aengelke created https://github.com/llvm/llvm-project/pull/171872

Single-use AddEmitPasses is inlined into RunCodegenPipeline for clarity
in comparing the parameters to the plugin and the parameters passed to
addPassesToEmitFile.