Build the dynamic way by default on Linux/amd64
This required various build system changes to get the build to go through. In the inplace shell wrappers, we set LD_LIBRARY_PATH to allow programs to find their libraries. In the future, we might change the inplace tree to be the same shape as an installed tree instead. However, this would mean changing the way we do installation, as currently we use cabal's installation methods to install the libraries, but that only works if the libraries are under libraries/foo/dist-install/build/..., rather than in inplace/lib/...