[clang] [Clang] Include LLVM CodeGen CMake file (PR #109601)

[Saleem Abdulrasool via cfe-commits]

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@@ -1,3 +1,7 @@
+if(EXISTS ${LLVM_MAIN_SRC_DIR}/include/llvm/CodeGen AND CLANG_BUILT_STANDALONE)
+  add_subdirectory(${LLVM_MAIN_SRC_DIR}/include/llvm/CodeGen llvm/lib/CodeGen)
+endif()
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compnerd wrote:

No, `LLVM_DIR` is passed to the CMake configure step to locate the build of LLVM. That should wire up the include path that should be needed either through a dependency on LLVMCodeGen or through a global include search path.

https://github.com/llvm/llvm-project/pull/109601