[clang] [clang] Extract in-memory module cache writes from `ASTWriter` (PR #190062)

[Lei Huang via cfe-commits]

lei137 wrote:

@jansvoboda11 Any update on this? I see this is still failing in our staging bot: https://lab.llvm.org/staging/#/workers/138

https://github.com/llvm/llvm-project/pull/190062