$ sudo apt-get update
$ sudo apt-get install gcc-msp430 

gcc-msp430 is installed in your system.

Make ensure the gcc-msp430 package were installed using the commands given below,

$ sudo dpkg-query -l | grep gcc-msp430 *

You will get with gcc-msp430 package name, version, architecture and description in a table

gcc-msp430 package basic information: