There are two locations where we check whether CMake supports
`TARGET_INCLUDE_DIRECTORIES`. While the first one uses `VERSION_LESS
2.8.12`, the second one uses `VERSION_GREATER 2.8.11`, which are
obviously equivalent to each other. It'd still be easier to grep for
specific CMake versions being required for some features if both used
the same conditional mentioning the actual target version required. So
this commit refactors these conditions to make them equal.
