cmake: consistently use TARGET_INCLUDE_DIRECTORIES if available

Instead of using INCLUDE_DIRECTORIES again for the libgit2_clar test
suite, we should just be using TARGET_INCLUDE_DIRECTORIES again if the
CMake version is greater than 2.8.11.

CMakeLists.txt

@@ -620,7 +620,6 @@ TARGET_OS_LIBRARIES(git2)
 
 IF (${CMAKE_VERSION} VERSION_LESS 2.8.12)
 	INCLUDE_DIRECTORIES(src include)
-	SET(LIBGIT2_INNER_DIRECTORIES_ARE_INCLUDED TRUE)
 ELSE()
 	TARGET_INCLUDE_DIRECTORIES(git2 PRIVATE src PUBLIC include)
 ENDIF()
@@ -694,12 +693,12 @@ IF (BUILD_CLAR)
 		${CLAR_PATH}/clar.c
 		PROPERTIES OBJECT_DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/clar.suite)
 
-	IF (NOT LIBGIT2_INNER_DIRECTORIES_ARE_INCLUDED)
-		INCLUDE_DIRECTORIES(src include)
-	ENDIF()
-
 	ADD_EXECUTABLE(libgit2_clar ${SRC_H} ${SRC_GIT2} ${SRC_OS} ${SRC_CLAR} ${SRC_TEST} ${SRC_ZLIB} ${SRC_HTTP} ${SRC_REGEX} ${SRC_SSH} ${SRC_SHA1})
 
+	IF (${CMAKE_VERSION} VERSION_GREATER 2.8.11)
+		TARGET_INCLUDE_DIRECTORIES(libgit2_clar PRIVATE src PUBLIC include)
+	ENDIF()
+
 	TARGET_LINK_LIBRARIES(libgit2_clar ${COREFOUNDATION_DIRS})
 	TARGET_LINK_LIBRARIES(libgit2_clar ${SECURITY_DIRS})
 	TARGET_LINK_LIBRARIES(libgit2_clar ${SSL_LIBRARIES})