mac 下获取 os x 的系统版本，使用 oc cocoa

#import <CoreServices/CoreServices.h>

SInt32 major, minor, bugfix;
Gestalt(gestaltSystemVersionMajor, &major);
Gestalt(gestaltSystemVersionMinor, &minor);
Gestalt(gestaltSystemVersionBugFix, &bugfix);

NSString *systemVersion = [NSString stringWithFormat:@"%d.%d.%d",
    major, minor, bugfix];

NSDictionary *systemVersionDictionary =
    [NSDictionary dictionaryWithContentsOfFile:
        @"/System/Library/CoreServices/SystemVersion.plist"];

NSString *systemVersion =
    [systemVersionDictionary objectForKey:@"ProductVersion"];