XCode多次预编译.pch

Question

我正在优化Xcode构建速度。从Travis构建日志中，我看到Xcode预编译了相同的pch文件4次。

  ✓ Precompile Pods-CKCountdownButton-CKCountdownButton-prefix.pch (1946 ms)
  ✓ Precompile Pods-CKCountdownButton-CKCountdownButton-prefix.pch (1935 ms)
  ✓ Precompile Pods-CKCountdownButton-CKCountdownButton-prefix.pch (1338 ms)
  ✓ Precompile Pods-CKCountdownButton-CKCountdownButton-prefix.pch (1307 ms)

可以找到完整的构建日志https://travis-ci.org/cybertk/CKCountdownButton/builds/31503539

如何通过仅预编译pch文件一次来减少构建时间？