[clang] [clang-tools-extra] [clang][modules] Serialize `CodeGenOptions` (PR #146422)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 commented:

This has a stronger impact on C++20 modules since C++20 modules need to generate codes. 

How does this patch handle consistency issue? e.g., What if `a.pcm` is compiled with `-O0` but the consumer is compiled with `-O1`? I hope we won't break such things.

https://github.com/llvm/llvm-project/pull/146422