aarch64-linux-gnu-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 CentOS possible default full paths are:

/usr/bin/aarch64-linux-gnu-as - from package: binutils-aarch64-linux-gnu

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/aarch64-linux-gnu-as - from package: binutils-aarch64-linux-gnu

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

Error in other languages:
aarch64-linux-gnu-as: bevel nie gevind nie
aarch64-linux-gnu-as: comandă negăsită
aarch64-linux-gnu-as: comando não encontrado
aarch64-linux-gnu-as: commande introuvable
aarch64-linux-gnu-as: command not found
aarch64-linux-gnu-as: käsku ei ole
aarch64-linux-gnu-as: không tìm thấy lệnh
aarch64-linux-gnu-as: komanda nerasta
aarch64-linux-gnu-as: Kommando nicht gefunden.
aarch64-linux-gnu-as: kommandot finns inte
aarch64-linux-gnu-as: komut yok
aarch64-linux-gnu-as: nie znaleziono polecenia
aarch64-linux-gnu-as: níor aimsíodh an t-ordú
aarch64-linux-gnu-as: no se encontró la orden
aarch64-linux-gnu-as: no s'ha trobat l'ordre
aarch64-linux-gnu-as: opdracht niet gevonden
aarch64-linux-gnu-as: parancs nem található
aarch64-linux-gnu-as: perintah tidak ditemukan
aarch64-linux-gnu-as: príkaz nenájdený
aarch64-linux-gnu-as: příkaz nenalezen
aarch64-linux-gnu-as: команда не найдена
aarch64-linux-gnu-as: командата не е открита
aarch64-linux-gnu-as: 命令找不到
aarch64-linux-gnu-as: コマンドが見つかりません