c++/6771: no code emitted for locally unused class with dllexport attribute

[Giovanni Bajo]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6771

I think it's again the usual regression in winnt.c (see pr/7910). The
problem appears to be fixed with 3.2 and a recent 3.3 CVS, but it causes an
ICE with 3.4 CVS 20030430. So I keep this as 3.4 ice-on-legal, in case it's
a slightly different issue.

Giovanni Bajo