[RFA/stabs] fix failed assertion during replacement of undefined type

[Daniel Jacobowitz]

On Thu, Apr 03, 2008 at 02:29:47PM -0700, Joel Brobecker wrote:
> The compiler ended up emitting the following debugging info for this
> type, which is incomplete:
> 
>     .stabs  "pck__data_t:t(0,32)=B(0,33)=xepck__data_t:",128,0,3,0

I think we should simply refuse this.  It's circular and obviously
broken.  We have a reference to a named type and the reference is
clearly intended to be to a non-volatile type, so GDB blowing up is
not entirely unreasonable.

That said, as you know, I care very little about the pathological
cases in our stabs parser; since no one more knowledgeable has
stepped up to object, this seems fine to commit.

-- 
Daniel Jacobowitz
CodeSourcery