Building with the pico-sdk requires gcc v9.1 or later

[mattytrentini]

Building MicroPython with GCC 8.5 raises a build error:

In file included from micropython/ports/rp2/machine_pwm.c:32,
                 from micropython/extmod/machine_pwm.c:50:
micropython/lib/pico-sdk/src/rp2_common/hardware_pwm/include/hardware/pwm.h: In function 'pwm_set_irq_mask_enabled':
micropython/lib/pico-sdk/src/rp2_common/hardware_pwm/include/hardware/pwm.h:658:55: error: expected ',' before ')' token
     static_assert(PWM_IRQ_WRAP_1 == PWM_IRQ_WRAP_0 + 1);

This is because GCC versions "prior to v9.1 do not support the single-argument static_assert".

I've confirmed that building with GCC v12.2 resolves the issue but I haven't tried with earlier versions (given the documentation I would assume it works with v9.1 but I have yet to try).

I suggest that either the code should be changed to add the second argument to static_assert - and thus work with earlier gcc versions - or document that v9.1 or later is required.