I have the Arduino 1.0.1 IDE installed.
This is Java based IDE not related to Code::Blocks at all. Why do you ask here?
The Arduino IDE is rather poor in terms of capability. Code::Blocks is a better alternative.
I have solved the problem. This project template of CodeBlocks may have a bug: In order to be able to select the UNO as the target, I must (when selecting the compiler) select both Create Debug and Release configurations. Selecting only one of them omits the UNO from the list of targets.