Did you try to compile it on the Raspberry Pi?
commands look something like:
sudo apt-get install git gcc-avr binutils-avr gdb-avr avr-libc avrdude
git clone https://github.com/MCUdude/optiboot_flash
cd optiboot_flash
./makeall
It builds on one of my Ubuntu 17.10 PC's, and the Raspberry works the same from what I have seen (it is not on the bench at the moment).