How to debug a target that requires build flags?

i have an executable target that must be built with special build flags:

swift run -c release -Xcc -mcx16 -Xswiftc -DENABLE_DOUBLEWIDE_ATOMICS MyTarget

how do i edit its launch configuration to build the target with those flags?

You can edit the build arguments in the settings for the extension. If you only want the arguments for that project you can edit the workspace settings from the same window.