Patch for --enable-checking ICE in div_trap on mips.

[Gavin Romig-Koch]

Geoff Keating writes:
 > 
 > This fixes an --enable-checking failure on MIPS.  I _think_ this is
 > what the code was trying to do.
 > 
 > OK to commit?

This is OK too.

                                   -gavin...