[clang] [clang][modules] Add single-module-parse-mode callback (PR #179714)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

Only the most recent commit is relevant here. The source branch is based on top of https://github.com/llvm/llvm-project/pull/179610.

https://github.com/llvm/llvm-project/pull/179714