debian/rules editconfigs fails on Raspberry Pi 4 with Ubuntu 20.04 aarch64

I’m trying to build a new kernel for Ubuntu 20.04 aarch64 on my Raspberry Pi 4.

Following the instructions in BuildYourOwnKernel from the Ubuntu Wiki, I get the following at the sudo LANG=C fakeroot debian/rules editconfigs step:

dh_testdir;
/bin/bash -e debian/scripts/misc/kernelconfig editconfigs
Do you want to edit config: armhf/config.flavour.raspi? [Y/n] n
make[1]: Entering directory '/home/john/picluster/kernel/linux-raspi-5.4.0'
make[2]: Entering directory '/home/john/picluster/kernel/linux-raspi-5.4.0/build'
  GEN     Makefile
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  LEX     scripts/kconfig/lexer.lex.c
  YACC    scripts/kconfig/parser.tab.[ch]
  HOSTCC  scripts/kconfig/lexer.lex.o
  HOSTCC  scripts/kconfig/parser.tab.o
  HOSTCC  scripts/kconfig/preprocess.o
  HOSTCC  scripts/kconfig/symbol.o
  HOSTCC  scripts/kconfig/conf.o
  HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf  --syncconfig Kconfig
scripts/Kconfig.include:35: compiler 'arm-linux-gnueabihf-gcc' not found
make[3]: *** [../scripts/kconfig/Makefile:73: syncconfig] Error 1
make[2]: *** [/home/john/picluster/kernel/linux-raspi-5.4.0/Makefile:594: syncconfig] Error 2
make[2]: Leaving directory '/home/john/picluster/kernel/linux-raspi-5.4.0/build'
make[1]: *** [Makefile:179: sub-make] Error 2
make[1]: Leaving directory '/home/john/picluster/kernel/linux-raspi-5.4.0'
make: *** [debian/rules.d/1-maintainer.mk:48: editconfigs] Error 2

I answered no to Do you want to edit config: armhf/config.flavour.raspi? [Y/n] n, anticipating being asked if I wanted to edit a config for arm64. I get the same message if I answer Y.

Any assistance would be much appreciated.

if [ "$variant" = "ports" ]; then
        archs=""
        family='ports'
else
        archs="arm64"
        family='ubuntu'
fi