[REPOST] MT-safe exception diffs for 971207

[Jason Merrill]

Looks great, thanks a lot!  Some minor comments:

In use_eh_context, why are you using copy_rtx on a REG rtx?  That's a nop.

I'm not sure why you need five functions to handle eh_context.

Indeed, the saved_pc stuff can be commented out ifdef DWARF2_UNWIND_INFO.
In fact, I'm about to blow away the old unwind code that uses saved_pc, so
you don't need to worry about making it work.  I'll be removing it just
after your patch goes in.

Why do you cast &eh->info and &eh->dynamic_handler_chain to their own
types?

Since you only use ptr_ptr_type_node once, there's no need to save it in a
global variable.

I'd just as soon put this patch in now and get a second patch for these
tweaks; Jeff?

Jason