Optiboot doesn't fit in 512 bytes when compiled with Toolchain 4 (Avr-gcc v15.x)

[WestfW]

Microchip has released a new "official" avr-gcc toolchain, based on avr-gcc v15.
The normal atmega328p optiboot grows by about 20 bytes, causing it to no longer fit in the 512byte boot sector we want to use.