The compiler provided in the external tools plugin is the one of the latest distributed in GNU ARM Embedded project (https://launchpad.net/gcc-arm-embedded). It has been built for Linux 32 bits and, as you said, needs the compatibility libs (libncurses, ...)
I don’t know which version of the compiler is distributed from the package manager. For the future version, we will rebuild the latest compiler version for 64 bits too.
By the way, if needed, you can use you own compiler by modifying the “path” setting in the project Properties > C/C++ Build > Settings > Tools settings > MCU Settings