I am using a workspace where I have a main app project and then a static library project which is used by the main app. I want static library project to spit out libX.a into
Go to File -> Project Settings.
Click the Advanced button under Derived Data Location. Under build location select custom and choose your output directory. This will change the variable $(BUILD_DIR) to whatever you set in that field.
Click done and go to your target settings. Under Build Location you can now specify where the targets are output based on that $(BUILD_DIR) macro.