message: After rL357618, quote ${CMAKE_THREAD_LIBS_INIT} so CMake does not
  complain when the variable is empty.  Fixes PR 41401.
diff: @@ -123,7 +123,7 @@ else()
  # Unfortunately the top-level cmake/config-ix.cmake file mangles CMake's
  # CMAKE_THREAD_LIBS_INIT variable from the FindThreads package, so work
  # around that, until it is fixed there.
  - if(${CMAKE_THREAD_LIBS_INIT} STREQUAL "-lpthread")
  + if("${CMAKE_THREAD_LIBS_INIT}" STREQUAL "-lpthread")
  set(OPENMP_TEST_COMPILER_THREAD_FLAGS "-pthread")
  else()
  set(OPENMP_TEST_COMPILER_THREAD_FLAGS "${CMAKE_THREAD_LIBS_INIT}")
  