[clang] [clang-repl] Fix PCH with delayed template parsing (PR #103028)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 approved this pull request.

Looks not bad. Let's land it after the CI gets green.

BTW, the delayed template parsing is a deprecated technique. Both clang and MSVC won't enable this after C++20 and we think it is the root of many bugs.

https://github.com/llvm/llvm-project/pull/103028