druntime implementation for the new ELF registration

 - Store thread local list of self-registering
   libraries. The compiler provides ModuleInfos
   and EH tables.

 - Use dl_iterate_phdr to get further information
   from the runtime linker.

 - Iterate over program headers
   to find writeable segments, i.e. the one with
   GC roots. The program header also provides
   TLS module indices and the TLS segment size.