Use ADDITIONAL_HEADER_DIRS in all LLVM CMake projects.

This allows IDEs to recognize the entire set of header files for
each of the core LLVM projects.

Differential Revision: http://reviews.llvm.org/D7526
Reviewed By: Chris Bieneman

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228798 91177308-0d34-0410-b5e6-96231b3b80d8
28 files changed