gcc-5-multilib software package provides GNU C compiler (multilib support), you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gcc-5-multilib
gcc-5-multilib is installed in your system.
Make ensure the gcc-5-multilib package were installed using the commands given below,
$ sudo dpkg-query -l | grep gcc-5-multilib *
You will get with gcc-5-multilib package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Development |
| Package | gcc-5-multilib |
| Version | 5.4.1-3 |
| Description | GNU C compiler (multilib support) |
| Sub Section | devel |