[IOS] Fix crash when launch item for play, if it built with xcode 4.

There's some static string defined in sdk 5+, I defined them if we are using xcode 3 to make it compilable, it's good, but when compile with xcode 4+, it links to the symbols in the sdk lib, so when running it on ios 4, the app can not find these strings (if compiled by xcode 3, it use the ones I defined in our code). so finally I has to prevent the part of code using these strings be called when running on ios 4. else will crash on ios 4 deviced (only if compiled by xcode 4+)