fix_includes: 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/fix_includes - from package: iwyu

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

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