This won't work...
Consider that regardless where you add `<define name="HOTT_SIM_GAM_SENSOR" value="1"/>` (or equally `<define name="HOTT_SIM_GAM_SENSOR" />`) it will result in a command line `-DHOTT_SIM_GAM_SENSOR=1` or `-DHOTT_SIM_GAM_SENSOR` option (hence having the same effect).
This also means that you can't have it in the makefile section AND in the airframe file.
Either don't define (the by default disabled ones) in the makefile section or use configure for the airframe file and makefile vars to set defaults (like for the uart).