STM32: Cpython compatibility flag

[hierophect]

Adds the MICROPY_CPYTHON_COMPAT flag to the STM32 port, which does not currently use the FULL_BUILD setting. Resolves #2433.

I think this might be a good opportunity to discuss the build settings in py/circuitpy_mpconfig.mk, since they're getting a little bloated. Right now we have:

• CIRCUITPY_FULL_BUILD (everything on the list)
• CIRCUITPY_SMALL_BUILD (just turns off full build only items)
• CIRCUITPY_DEFAULT_BUILD (everything not in full build)
• CIRCUITPY_MINIMAL_BUILD (turns off default build items)
• CIRCUITPY_ALWAYS_BUILD (items with no HAL component that always get built)

Would it be simpler here to remove the "turn off" flags and have ports define the highest level they want to include? IE just three items, FULL_BUILD, DEFAULT_BUILD, MINIMAL_BUILD. py/circuitpy_mpconfig.h would be changed to detect the absence of FULL_BUILD.

[dhalbert]

I agree the BUILD flags should be tuned up (I was thinking of ALWAYS, MINIMAL, 192kB, 256kB, FULL). Worth opening an issue, but not urgent.

[dhalbert]

👍