假设不小心改动了系统SDK文件，编译无法通过改怎么办？（iOS开发）

 project报例如以下错误：

fatal error: file '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/

Developer/SDKs/iPhoneSimulator8.0.sdk/usr/include/sysexits.h' has been modified since the 

precompiled header '/Users/Lycros/Library/Developer/Xcode/DerivedData/ModuleCache/NZL05J5PKZ6B/

***.pch.pch' was built 

解决方案例如以下：

Quit Xcode and remove everything in the module cache located here:

~/Library/Developer/Xcode/DerivedData/ModuleCache （删除该文件里的缓存就可以）

The cache that was built with a previous version of Xcode is invalid for this version of Xcode and SDK, and that is causing your error