Rename CMake's Boost_USE_ICU to WITH_BOOST_ICU (update your CMake conf if you make static builds!), and add it as CMake option.

Patch by gdh (Gavin Howard), many thanks!

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54795 954f8c5b-7b00-dc11-b283-0030488c597c