[PATCH] [CMake] Update required version to 2.8.12 to improve build time with target_link_libraries(INTERFACE)

[NAKAMURA Takumi]

  Argyrios, I'd be happy if this feature worked as optional.

  Brad, any good idea?
  Could I twiddle cmake_minimum_required and cmake_policy explicitly there?

http://llvm-reviews.chandlerc.com/D2864