[clang] [C++20] [Modules] [Driver] Don't enable -fdelayed-template-parsing by default on windows with C++20 modules (PR #69431)

[Reid Kleckner via cfe-commits]

rnk wrote:

We can definitely disable delayed template parsing in C++20 mode, I wouldn't argue against that. Whoever actually does the work should decide how much effort they are willing to put in. I'm just saying there are benefits to starting the deprecation clock sooner, since it will ultimately reduce tech debt sooner, and avoid additional confusing behavior differences between C++17 and C++20. I think all it takes is an extra RFC and a release note.

https://github.com/llvm/llvm-project/pull/69431