iOS报错 -pie can only be used when targeting iOS 4.2 or later

近期，使用师兄的project时。突然报错之前没发现这个错误。信息例如以下：

ld: -pie can only be used when targeting iOS 4.2 or later

clang: error: linker command failed with exit code 1 (use -v to see invocation)

详细信息：

    export IPHONEOS_DEPLOYMENT_TARGET=4.1

    export PATH="/Applications/Xcode.a

解决方法：点击工程project-》build setting --》搜索IPHONEOS_DEPLOYMENT_TARGET 改动为4.2以后