c/9928: [3.3/3.4 regression] ICE on duplicate enum declaration

[Steven Bosscher]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9928

This PR was introduced with Eric's patch that fixed another ICE (for 
c/7741):
http://gcc.gnu.org/ml/gcc-patches/2003-02/msg00641.html

So we've exchanged one ICE for another :-)

Greetz
Steven