INCLUDE (CheckCXXSourceCompiles)
unset(STXXL_WORKS CACHE)
set (STXXL_CHECK_SRC "#include <stxxl/vector>\n int main() { stxxl::vector<int> vec; return 0;}")
set (CMAKE_TRY_COMPILE_CONFIGURATION ${CMAKE_BUILD_TYPE})
set (CMAKE_REQUIRED_INCLUDES "${STXXL_INCLUDE_DIR}")
set (CMAKE_REQUIRED_LIBRARIES "${STXXL_LIBRARY}")

CHECK_CXX_SOURCE_COMPILES("${STXXL_CHECK_SRC}" STXXL_WORKS)

if(STXXL_WORKS)
  message(STATUS "STXXL can be used without linking against libgomp")
else()
  message(STATUS "Linking STXXL failed without libgomp, retrying ..")
  find_package(OpenMP)
  set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}${OpenMP_CXX_FLAGS}")
  CHECK_CXX_SOURCE_COMPILES("${STXXL_CHECK_SRC}" STXXL_LINKS)

  if (STXXL_LINKS)
    message(STATUS "STXXL needs to link against OpenMP")
    target_link_libraries(osrm-extract gomp)
  else()
    message(FATAL_ERROR "STXXL failed failed, libgomp missing?")
  endif()
endif()