Update libiberty demangler to support Rust v0 name mangling

Update libiberty demangler to support Rust v0 name mangling

Update the libiberty demangler using the auxprogs/update-demangler
script to the gcc git 01d92cfd79872e4cffc78bf233bb9b767336beb8.
Updates rust demangling to support the new v0 mangling scheme.

This includes the following changes:
- Update the update-demangler script to use gcc git instead of svn.
- The result of running the updated script to get an updated
  demangler and resolving the merge conflicts.
- A change to long_namespace_xml.stderr.exp because two overly long
  symbols aren't demangled anymore, but just returned as is.
- an update to the m_demangle/demangle.c source to deal with Rust
  demangling in cp_demangle, which now directly demangles old and
  new style rust symbols.