message: Add support for LOCAL_LLVM_DIR
diff: -FetchContent_Declare(
  - llvm-project
  - URL https://github.com/plaidml/llvm-project/archive/182eb478559f27191b7373616f30a608065aaaa3.tar.gz
  - URL_HASH SHA256=606ce4fae35c72b951f31402741403d568287933712db5ae4e735e51b00bab46
  -)
  -
  set(LLVM_APPEND_VC_REV OFF CACHE BOOL "" FORCE)
  set(LLVM_ENABLE_IDE OFF CACHE BOOL "" FORCE)
  set(LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "" FORCE)
  @@ -19,6 +13,18 @@ set(OPENMP_ENABLE_LIBOMPTARGET OFF CACHE BOOL "" FORCE)
  set(OPENMP_ENABLE_OMPT_TOOLS OFF CACHE BOOL "" FORCE)
  set(OPENMP_STANDALONE_BUILD ON CACHE BOOL "" FORCE)
  +message("LOCAL_LLVM_DIR: ${LOCAL_LLVM_DIR}")
  +
  +if(LOCAL_LLVM_DIR)
  + set(LLVM_SOURCE_DIR ${LOCAL_LLVM_DIR})
  + set(LLVM_BINARY_DIR ${CMAKE_BINARY_DIR}/_deps/llvm-project-build)
  + add_subdirectory(${LLVM_SOURCE_DIR}/llvm ${LLVM_BINARY_DIR} EXCLUDE_FROM_ALL)
  +else()
  + FetchContent_Declare(
  + llvm-project
  + URL https://github.com/plaidml/llvm-project/archive/182eb478559f27191b7373616f30a608065aaaa3.tar.gz
  + URL_HASH SHA256=606ce4fae35c72b951f31402741403d568287933712db5ae4e735e51b00bab46
  + )
  FetchContent_GetProperties(llvm-project)
  if(NOT llvm-project_POPULATED)
  FetchContent_Populate(llvm-project)
  @@ -26,7 +32,7 @@ if(NOT llvm-project_POPULATED)
  set(LLVM_BINARY_DIR ${llvm-project_BINARY_DIR})
  add_subdirectory(${LLVM_SOURCE_DIR}/llvm ${LLVM_BINARY_DIR} EXCLUDE_FROM_ALL)
  endif()
  -
  +endif()
  list(APPEND LLVM_INCLUDE_DIRS
  ${LLVM_SOURCE_DIR}/llvm/include
  