RFC/RFHelp: c-decl.c rewrite - almost but not quite

[Robert Bowdidge]

> Here finally is the big c-decl.c rewrite.  I'm pleased to report it
> solves the infamous dwarf2out ICE and several other bugs (see the
> changelog for details).  However, I need some help finishing it.
>
> Most significantly, the Objective-C and possibly Java front ends
> appear to be broken by this patch, such that neither runtime library
> can be built.  For Objective-C the symptoms are a bunch of warnings
> about unexpected types for 'id' followed by an ICE in list_length
> owing to a list of global decls that has somehow become circular.
> (I added circular list detection to list_length under ENABLE_CHECKING;
> without that it would be an infinite loop instead of an ICE.)

Considering this is a 4000 line diff, could you give a high-level
description of how the code's changed architecturally?  Your previous
c-decl.c changes did a pretty nice job of explaining what was going on
in each change ("another coffee spoon of progress on c-decl.c" from
March 9 and "RFC/PATCH: c-decl.c: no getdecls() for you" from Feb. 8,
or "c-decl.c overhaul (1/3) Refactor duplicate_decls" from Jan. 10)

We're mucking in potentially similar code on the C++ side for the stree
work, and it would be understand how this work might conflict with
ours.

Robert