直接引用老外的问题描述：

I can't install php71 with brew install php71 --with-httpd as an error appears during the make process :
ld: file not found: /usr/lib/system/libsystem_darwin.dylib for architecture x86_64

如下即可解决！

I just did a clean install of MacOS Sierra (10.12.6) and had this same issue. I installed homebrew before Xcode was fully downloaded. I noticed that homebrew downloaded and installed the command line tools itself. I'm not sure if that's was caused the problem, but here's how I fixed it:
Removed the command line tools
sudo rm -rf /Library/Developer/CommandLineTools
Reinstalled the command line tools via xcode
xcode-select --install
Set the correct path
xcode-select -s /Library/Developer/CommandLineTools
Then the php7 install works fine
brew install php71 --with-httpd

原文链接：点击访问