[RFA] symtab.c: Fix for infinite GDB recursion in gdb.c++/classes.exp

[Peter.Schauer]

> > Unfortunately this is not covered by the testsuite, but I will try to come
> > up with an example.
> You won't be able to, we convert psymtabs to symtabs too often, so
> you'd have to find a way to have it not do the conversion for your
> particular psymtab.

And, just for fun, try
maint check
on gdb.c++/misc, with and without your changes.

-- 
Peter Schauer			pes@regent.e-technik.tu-muenchen.de