XCODE5.0升到XCODE5.1后LLVM也从5.0升到5.1，工程报下面的错误了:
clang: error: unknown argument: '-fobj-arc' [-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 Command /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang failed with exit code 1从Xcode Release Notes找到说明
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. Projects using invalid compiler options will need to be changed to remove those options. To help ease that transition, the compiler will temporarily accept an option to downgrade the error to a warning:将target-build phases-中'-fobj-arc'改成'-fobjc-arc'。