message: Remove "-lpthread" when building tests on macos.
  In most cases it seems to be not used.
diff: @@ -641,6 +641,9 @@ def tf_cc_test(name,
  ],
  clean_dep("//tensorflow:windows"): [],
  clean_dep("//tensorflow:windows_msvc"): [],
  + clean_dep("//tensorflow:darwin"): [
  + "-lm",
  + ],
  "//conditions:default": [
  "-lpthread",
  "-lm"
  