SDL 2.0.0 supports iOS 5.1.1 or newer. Older versions of SDL support iOS 3.1.3 or newer.
For the latest information see the page about Installation.
Go to the Xcode menu Project -> Edit Project Settings, scroll down to the Linking section, and add -ObjC to the "Other Linker Flags" option. If you have target specific settings for your linker flags, you'll need to add this at the target level instead, by right clicking the target and selecting the "Get Info" menu option.
These devices are probably using the ARMv6 architecture instead of the ARMv7 architecture. Try changing your "Active Architecture" to ARMv6 in the Xcode main project window.