GNAT project files have the concept of scenario variables that allow considerable flexibility in controlling how the tools build an executable. (See Scenario Variables for details on scenario variables, and GNAT Projects for the details of GNAT project files.) You can define, for example, different scenarios for debugging and releases, in which optimization and symbolic information are either present or not, respectively.
GNATbench provides the Scenario View for managing scenario variables. The idea is that you can control the build by changing the values of the scenario variables within this view. (See Scenario View for details.)