VS: CMake 3.20.0-rc1 breaks per-language PCH

My project uses this line target_precompile_headers(${APP_PROJECT} PRIVATE "$<$<COMPILE_LANGUAGE:CXX>:${pch}>") which means I want only .cpp files to use precompiled headers. My project has a few .c files. Since CMake 3.20 those files are now using precompiled headers!

Additional problems: as a workaround I added precompiled headers also for C language and the problem was gone. However MSVC now emits warning 4206 about empty translation unit for file cmake_pch.c

I am using MSVC 16.8.5