codal_port/Makefile: Keep C/C++ flags set up by MicroPython lib.

[microbit-carlos]

This to be able to create C/C++ modules without modifying files in this repository, as shown in https://github.com/microbit-foundation/micropython-cpp-module-example.

Comparing the flags used before and after this patch:

• The flags generated in the built CMake output files are the same, as those are managed by the CODAL build system
• In the MicroPython c files, the only difference was the addition of -DFFCONF_H=\"lib/oofatfs/ffconf.h\" define
  • From micropython/extmod/extmod.mk#L177
• The makeqstrdefs.py invocation added more flags with the CODAL include paths, my assumption being that this probably won't matter that much if it's only for the qstr generation

The makeqstrdefs.py extra flags added:

-I. -I../codal_app -I../../lib -I../../lib/codal/libraries/codal-nrf52/inc/cmsis -I../../lib/codal/libraries/codal-nrf52/nrfx -I../../lib/codal/libraries/codal-nrf52/nrfx/drivers/include -I../../lib/codal/libraries/codal-nrf52/nrfx/hal -I../../lib/codal/libraries/codal-nrf52/nrfx/mdk -I../../lib/micropython -I../../lib/micropython/ports/nrf

[dpgeorge]

This change looks good to me. This is how we do it in MicroPython itself (use += for most Makefile variables).

[dpgeorge]

This to be able to create C/C++ modules without modifying files in this repository

That's a good example!