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

[Maksim Levental via llvm-commits]

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@@ -79,6 +79,48 @@ function(llvm_update_compile_flags name)
   target_compile_definitions(${name} PRIVATE ${LLVM_COMPILE_DEFINITIONS})
 endfunction()
 
+function(llvm_update_pch name)
+  if(LLVM_REQUIRES_RTTI OR LLVM_REQUIRES_EH)
+    # Non-default RTTI/EH results in incompatible flags, precluding PCH reuse.
+    set(ARG_DISABLE_PCH_REUSE ON)
+  endif()
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makslevental wrote:

Ah sorry I read too quickly (I misread these flags as `LLVM_ENABLE_RTTI` and `LLVM_ENABLE_EH`). Makes sense. Thanks.

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