exclude fpu options from stm32wl55

[dolfandringa]

Summary

This PR fixes bug

• STM32WL platformio options for cortex-m4 turn on fpu, but STM32WL55 CMSIS driver defines __FPU_PRESENT=0 #1473

Arduino Core STM32 provides a platformio-build.py file that sets compiler build flags for Arduino Core STM32 in platformio. This file sets the -mfpu flag automatically for every cortex-m4 MCU. But according to the CMSIS drivers, the STM32WL55 does not contain an FPU, causing this python script to set the wrong compile time flags. The proposed PR fixes this by excluding the -mfpu option from the CPPDEFINES flags.

Validation

• Ensure CI build is passed.
  The following sketch won't compile without it, but will with this fix:

#include <Arduino.h>

void setup() {
}

void loop() {
}

Closing issues

Fixes #1473

[fpistm]

Please @valeros could you review this?

[valeros]

Hi @dolfandringa ! Many thanks for the PR. Please review my comments above.

[dolfandringa]

With this PR, and the one I am submitting for platformio, I got a basic blink sketch to compile, upload and (gdb) debug correctly on the nucleo stm32wl55JC1.

[valeros]

LGTM.

[fpistm]

Thank you @valeros and @dolfandringa