cmake: unify version check for target include directories

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.

tests/CMakeLists.txt

@@ -37,7 +37,9 @@ ADD_EXECUTABLE(libgit2_clar ${SRC_CLAR} ${SRC_TEST} ${LIBGIT2_OBJECTS})
 
 SET_TARGET_PROPERTIES(libgit2_clar PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})
 
-IF (${CMAKE_VERSION} VERSION_GREATER 2.8.11)
+IF (${CMAKE_VERSION} VERSION_LESS 2.8.12)
+	# Already handled by a global INCLUDE_DIRECTORY()
+ELSE()
 	TARGET_INCLUDE_DIRECTORIES(libgit2_clar PRIVATE ../src PUBLIC ../include)
 ENDIF()