[clang] [flang] [llvm] [mlir] [polly] [CMake][LLVM] Add PCH infrastructure and LLVMSupport PCH (PR #176420)

[Jakub Kuderski via cfe-commits]

================
@@ -12,4 +12,6 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsAddObjectFile
   OrcV2CBindingsAddObjectFile.c
+
+  DISABLE_PCH_REUSE # no C++ files, prevent CMake error.
----------------
kuhar wrote:

nit:
```suggestion
  DISABLE_PCH_REUSE # No C++ files, prevent CMake error.
```

also everywhere else

https://github.com/llvm/llvm-project/pull/176420