[PATCH 0/5] MR7811: PDB rewrite #8.

[eric pouech (＠epo)]

This serie starts moving type handling into PDB backend.

In order to handle both the existing symt_{*} structures for
every debug info objects and their potential counterpart
inside a debug info backend, we introduce an opaque symref_t
which can either hold a pointer or a value dedicated to a
debug backend.

This allows:
- to have generic code handling transparently a debug info
  object (whether it's managed as a symt_{*} object, or
  as a reference in backend)
- during the migration phase from old to new PDB backend,
  to select, by type of object, whether it's handled by
  old or new backend, hence allowing a migration scheme
  by type of object.

This series mainly introduces the symref_t instead of
the existing pointer to symt_{*}.