all makefiles: use -fshort-enums to save some memory

This adds -fshort-enums to all target makefiles which tells gcc to make each individual enum use the smallest possible integer type to hold all its values. This breaks compatibility to code which has not been compiled using -fshort-enums.

The intent of this is to save memory on the flight side.

Todo:
* test and record memory usage on F1
* test on F3
* test on F4