[llvm] [CMAKE][llvm-libraries] Add Precompiled Headers option to improve build times (PR #91755)

[Volodymyr Sapsai via llvm-commits]

vsapsai wrote:

As for the modules, clang modules work but they require clang to be the compiler. So it won't work with MSVC compiler. Not sure C++20 modules would work (don't know about any bots testing this configuration) but we don't support a sufficiently new CMake. In addition, clang's support of C++20 modules isn't complete, so I don't think that C++20 modules is a viable alternative to the precompiled headers at this time.

I also have to admit that I have a selfish interest in comparing modules' performance with PCH and glad that I don't need to provide PCH part myself.

https://github.com/llvm/llvm-project/pull/91755