IOS 版本控制判断

// 版本判断
#define SYSTEM_VERSION(ver) [[[UIDevice currentDevice] systemVersion] compare:ver] != NSOrderedAscending
#define IOS9_OR_LATER SYSTEM_VERSION(@"9.0")
#define IOS8_OR_LATER SYSTEM_VERSION(@"8.0")
#define IOS7_OR_LATER SYSTEM_VERSION(@"7.0")