在我的Mac Air上，用pip安装一些Python库时，偶尔就会遇到一些报错，关于“unused-command-line-argument-hard-error-in-future”，错误如下：
clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
error: command 'cc' failed with exit status 1
这样的错误，出现次数多了，每次都去google，不如自己记录一下吧。
原因是：The Apple LLVM compiler in Xcode 5.1 treats unrecognized command-line options as errors. This issue has been seen when building both Python native extensions and Ruby Gems, where some invalid compiler options are currently specified.
解决方法：设置ARCHFLAGS参数，如下:
