[clang] [clang-tools-extra] [clang][Serialization] Serialize DiagStateOnPushStack to fix pragma d… (PR #190420)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> Thanks everyone for the reviews and discussion! It sounds like there's consensus to land this patch.
> 
> @HighCommander4 @ArcsinX @ChuanqiXu9 would any of you be able to approve & merge this PR? I don't have write access yet.
> 
> Regarding the `#pragma pack(push, 1)` issue @ArcsinX raised — I'm happy to investigate that separately and submit a follow-up PR if needed.

Before approving I want to say my feeling for this. I can accept one workaround. But if we have multiple workarounds for the same kind of issue (unpaired #pragma ) , it is not good. If we want to workaround this kind of issues, we need to have a mechanism to solve this kind of problem generally. 

Otherwise, it may not to be bad too just error out.

https://github.com/llvm/llvm-project/pull/190420