Strip optional runtimes and shared libraries from the system

[mobileoverlord]

This was inspired by the issue at nerves-project/toolchains#45

Adding additional tools to the toolchains can cause the systems to include additional shared libraries and runtimes. In the example above, enabling fortran in the toolchain would cause the system to be built with support for running fortran.

The idea would be to provide a mechanism for stripping out these files that would not be necessary on targets that do not use them.