[CMake] Introduce cmake_policy(CMP0022) for target_link_libraries(INTERFACE|PRIVATE).

For now, use both keywords, INTERFACE and PRIVATE via the variable,
  - ${cmake_2_8_12_INTERFACE}
  - ${cmake_2_8_12_PRIVATE}

They could be cleaned up when we introduce 2.8.12.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202239 91177308-0d34-0410-b5e6-96231b3b80d8