How can I add older version of iOS SDK in Xcode

I create a Iphone app is working fine in the iOS 5.1 sdk but now in iOS 6.1 sdk.  Then i update my Xcode to 4.6.1 now what happen i sort out  the app issue but when i am trying to submit the app was trying to build the ipa file it gave an error

Apple Mach-o linker error

 linker command failed with exit code 1 (use -v to see invocation)

Here is my solution note.

1. Download xcode_4.4.1_6938145.dmg in https://developer.apple.com/downloads/
2. Load up the dmg file then go to Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/ you will find iPhoneOS5.1.sdk (this is what i want in this case).
3. Copy iPhoneOS5.1.sdk folder into your Xcode folder /Applications/Xcode/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs
4. Restart Xcode
5. Open Xcode project setting->build settings->base SDK, then you will see iOS 5.1 option.

You need to copy the iPhoneOS5.1.sdk to the directory

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk

and iPhoneSimulator5.1.sdk to

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.1.sdk

Now restart your Xcode change the iOS to 6.1 to 5.1 THen it will compile the app into your iPhone. if it is helpful then post a comment below.