For the 3 ports that already make use of this feature (stm32, nrf and
teensy) this doesn't make any difference, it just allows to disable it from
now on.
For other ports that use pyexec, this decreases code size because the debug
printing code is dead (it can't be enabled) but the compiler can't deduce
that, so code is still emitted.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.