llvm

ca155dbe - [clang] Enable wrapping the FrontendAction for module builds (#184907)

[clang] Enable wrapping the FrontendAction for module builds (#184907) This PR upstreams a piece of infrastructure from Swift's LLVM fork. This allows adding custom wrappers around the `FrontendAction` that compiles Clang modules from a module map into a PCM file. This will be used to implement modules support in the CAS-based compilation caching mode.