I noticed that gdb-arm-none-eabi package is not present on Ubuntu 18.04 repository. After some searches I saw people suggesting to use gdb-multiarch, but this gdb didn’t work for me.
Then after more some searching I found the solution is easy: just download and install this package from Xenial (Ubuntu 16.04) :
$ sudo dpkg -i libreadline6_6.3-8ubuntu2_amd64.deb
$ sudo dpkg -i gdb-arm-none-eabi_7.10-1ubuntu3+9_amd64.deb