[unittest] Add CMAKE_BUILD_DIR/unittest as an include directory.

unittest/CMakeLists.txt

@@ -58,6 +58,7 @@ ADD_DEFINITIONS(-DDEBUG=2)
 
 # Add MatrixAbstractLayer compilation flags
 INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/include)
+INCLUDE_DIRECTORIES(${CMAKE_BINARY_DIR}/unittest)
 
 FOREACH(test ${tests})
   GET_FILENAME_COMPONENT(EXECUTABLE_NAME ${test} NAME)