[clang] Reset CodeGenOptions fields for clean module/PCH builds (PR #138256)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

hmmm for `test case`, I mean a test case in clang, either a unit test or a lit test, so we can understand the effect on users more clearly. 

And if you're talking about the general code policy, I'll suggest you to https://discourse.llvm.org/ to make it more verbose.

https://github.com/llvm/llvm-project/pull/138256