target/3947: [MIPS] MIPS multiple inheritance - thunk causes two destructor calls

[Tim Small]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=3947

This bug should prob be reclassified as non-architecture dependent, as 
we are seeing this bug (or at least one with the same effect) on i386. 
 Is it worth us trying to whittle down to the smallest code snippet 
necessary to reproduce this (we are working with a fairly large closed 
source base so this may be quite time consuming - no problem doing it, 
but wanted to check if it is actually going to be useful?).

Cheers,

Tim.