[RFA 0/6] Make psymbols independent of the progspace

[Tom Tromey <tom@tromey.com>]

This is another old patch series that I never checked in, which I've
now rebased.

Like some earlier series -- most recently for line tables -- This
series changes partial symbols to be independent of the progspace.
This means that the data is now stored unrelocated, and could in
theory be shared across multiple objfiles.

In practice psymtabs cannot be shared yet, because they have a
backlink to the full symtab.

Patches #1-#3 are just infrastructure changes in preparation for the
main patch; and most of the real work is in patch #6.

In patch #6 I chose to adjust addresses like this:

      lo = gdbarch_adjust_dwarf2_addr (gdbarch, lo + baseaddr) - baseaddr;

I'm not sure if this is the best way.  Maybe in the line table (I
can't look at this moment and I don't recall offhand) patch I chose to
pass unrelocated addresses to gdbarch_adjust_dwarf2_addr.  It would be
good to nail down the intended meaning of this hook and adjust
accordingly.

Tested by the buildbot -- but careful review is still required,
because some of the changes are not tested there.

Tom