[PATCH][C++] Fix dump-file corruption

[Paolo Bonzini]

> Fixed by moving (swapping) a cached decls name to the position it would
> have had if it had been freshly allocated.  This ensures that we can
> reliably print strings with at least RING_SIZE decl names in them.

I think you fail if you are printing three strings, with the first one 
not in the cache, the second at the last place in the cache, and the 
third one not in the cache.  The third cxx_printable_name will expunge 
the output of the first.

You really need LRU.

Paolo