我想提供我的Objective-C库作为cocoapod，有些用户希望使用'use_frameworks'来获取它选项。如果没有这个键，它可以正常工作，但在将其包含在Podfile中后，Xcode 7.1 Beta会抛出这些错误：
Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_***", referenced from:
objc-class-ref in ***.o
"_OBJC_CLASS_$_***", referenced from:
_OBJC_CLASS_$_*** in ***.o
objc-class-ref in ***.o
objc-class-ref in ***.o
(maybe you meant: _OBJC_CLASS_$_***)
"_OBJC_CLASS_$_***", referenced from:
objc-class-ref in ***.o
objc-class-ref in ***.o
objc-class-ref in ***.o
"_OBJC_METACLASS_$_***", referenced from:
_OBJC_METACLASS_$_*** in ***.o
(maybe you meant: _OBJC_METACLASS_$_***)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)