external-luajit: added fix for older cmake's

cmake/luajit.cmake

@@ -40,10 +40,12 @@ macro (luajit_test)
     if (${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
         set (CMAKE_REQUIRED_LIBRARIES "-ldl ${CMAKE_REQUIRED_LIBRARIES}")
     endif()
+    set (CMAKE_REQUIRED_INCLUDES "${LUAJIT_INCLUDE}")
     CHECK_CXX_SOURCE_RUNS ("${LUAJIT_TEST}" LUAJIT_RUNS)
     set (LUAJIT_TESTED "${LUAJIT_RUNS}")
     unset (LUAJIT_RUNS)
     unset (CMAKE_REQUIRED_LIBRARIES)
+    unset (CMAKE_REQUIRED_INCLUDES)
 endmacro()
 
 #
@@ -77,7 +79,6 @@ macro (luajit_try_prefix)
     luajit_find(False)
     if (LUAJIT_INCLUDE AND LUAJIT_LIB)
         include_directories("${LUAJIT_INCLUDE}")
-        link_directories("${LUAJIT_PREFIX}")
         luajit_test()
         if (LUAJIT_TESTED)
             message (STATUS "Supplied luajit is suitable for use.")