c-index-test: 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/c-index-test - from package: clang

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

On Debian possible default full paths are:

/usr/bin/c-index-test - from package: clang
/usr/lib/llvm-3.4/bin/c-index-test - from package: clang-3.4
/usr/lib/llvm-3.5/bin/c-index-test - from package: clang-3.5

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

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