[flang] [llvm] [flang] Use precompiled headers in Frontend, Lower, Parser, Semantics and Evaluate (PR #131137)

[Kajetan Puchalski via llvm-commits]

mrkajetanp wrote:

With #136856 merged there is now proper ccache support for this on Linux. I added a line here to disable pch on Windows for the time being, meaning this should now be ready to go.

https://github.com/llvm/llvm-project/pull/131137