Xcode10删除libstdc++库编译报错

Xcode10中删除了`libstdc++`库，导致老项目在Xcode11中编译失败，解决方法如下：

`libstdc++`库下载链接：https://pan.baidu.com/s/1y08On0bQo-v7Me7_rYIi-g。

或者点击—> libstdc++库

其中文件夹 1、2、3、4 中的文件分别对应复制到Xcode中的以下4个目录中即可：

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib/

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/lib/