make: g++: Command not found Reading the output should is something that you should learn to do. Especially when things aren't going as planned.
Depending on your flavor of Linux. Use the package manager and install the gcc package.
Arch Linux: pacman -Syu gcc
Ubuntu/Debian/Mint: apt-get install gcc
(you may also need to install build-essential
)
Fedora: yum install gcc gcc-c++
or yum groupinstall "Development Tools"
(for all dev tools)
After installing the compiler rerun the gem installation and it should be fine unless you're missing other dependencies