Default to the medium code model in x86 linux (#53391)
This shouldn't have any cost on smaller images because the only thing
that gets put into ldata is the system image data, which is only
reference via `dlsym`. This allows for images larger than 2gb (tested by
putting a 2gb array in the base image)
I did not test how this might be handled in other platforms (Windows
doesn't support it).
