Building on vanilla 64-bit Raspbian bullseye doesn't work

[MichaelBell]

Building with the default arm-none-eabi toolchain installed from Raspbian bullseye produces an image that's significantly too large to work. Raspbian bullseye has a debian modified version of 8.3.1.

Downloading 9.2.1 from the Arm website and specifying that as the toolchain produces a good build.

Note that using 10.3.1 produces a smaller overall build but overflows SCRATCH_X (and just reducing the defined CORE1 stack size doesn't fix this as it is already set at the minimum value).