druntime implementation for the new ELF registration

- Store information from self-registering libraries. The compiler
  provides ModuleInfos and EH tables.
reference _d_dso_registry for weak-linkage

- because we're linking against archives the linker
  would never read the rt/dso.o object file
Merge pull request #397 from dawgfoto/SharedRuntime_2

druntime implementation for the new ELF registration