[clang] [serialization] no transitive decl change (PR #92083)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

The 10x increase in the time spent reading modules does look surprising and I would need to check if it's related to PCMs becoming larger or is localized to that particular compile. (Even if on a single example).

@ChuanqiXu9 do you expect alignment to have such a drastic effect on deserialization time? That would be very surprising to me.
The reproducer will take time, could we revert in the meantime?

https://github.com/llvm/llvm-project/pull/92083