MacOS C编译环境出现问题
原因：
我之前卸载过Xcode出现的
Jerry:~ Jerry$ gcc
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
解决方案：
Jerry:~ Jerry$ xcode-select --install
xcode-select: note: install requested for command line developer tools
