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

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

Agree with @ArcsinX , I feel the current preamble PCH deciding logic is somewhat fragile.

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