ICU_INCLUDE_DIRS for cli projects

[emabiz]

Hi, first of all thank you for your work about Tokenizer and CTranslate2.

I tried to compile Tokenizer under win10. It works fine except I had to modify the include part in the main CmakeLists.txt

set(INCLUDE_DIRECTORIES
  PUBLIC
  ${CMAKE_CURRENT_SOURCE_DIR}/include
  ${PROJECT_BINARY_DIR}
  ${ICU_INCLUDE_DIRS}

  PRIVATE  
  ${CMAKE_CURRENT_SOURCE_DIR}/third_party/sentencepiece/src
  )

putting ${ICU_INCLUDE_DIRS} in the public section, because it is used also by cli projects and putting it in the private section doesn't propagate the value to these projects. Is it expected?

Emanuele