z80-unknown-coff-as: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/z80-unknown-coff-as - from package: binutils-z80

You may install the required package with command apt-get install {package}

Error in other languages:
z80-unknown-coff-as: bevel nie gevind nie
z80-unknown-coff-as: comandă negăsită
z80-unknown-coff-as: comando não encontrado
z80-unknown-coff-as: commande introuvable
z80-unknown-coff-as: command not found
z80-unknown-coff-as: käsku ei ole
z80-unknown-coff-as: không tìm thấy lệnh
z80-unknown-coff-as: komanda nerasta
z80-unknown-coff-as: Kommando nicht gefunden.
z80-unknown-coff-as: kommandot finns inte
z80-unknown-coff-as: komut yok
z80-unknown-coff-as: nie znaleziono polecenia
z80-unknown-coff-as: níor aimsíodh an t-ordú
z80-unknown-coff-as: no se encontró la orden
z80-unknown-coff-as: no s'ha trobat l'ordre
z80-unknown-coff-as: opdracht niet gevonden
z80-unknown-coff-as: parancs nem található
z80-unknown-coff-as: perintah tidak ditemukan
z80-unknown-coff-as: príkaz nenájdený
z80-unknown-coff-as: příkaz nenalezen
z80-unknown-coff-as: команда не найдена
z80-unknown-coff-as: командата не е открита
z80-unknown-coff-as: 命令找不到
z80-unknown-coff-as: コマンドが見つかりません