打开终端输入：xcode-select --install 回车
安装好了测试结果：gcc -v
显示如下：
xcode-select: note: install requested for command line developer tools
apple-1tekiiMac:~ apple-1$ gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.1.0 (clang-602.0.49) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix