我正在使用xcode 7，当我构建时，我面临这个问题
Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_GMSServices", referenced from:
objc-class-ref in AppDelegate.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
有什么遗漏的吗？