Per a discussion with Alan...

update_equiv_regs now tests that the insn which creates an equivalence 
dominates its uses.  With one exception, if may_trap_p returns false, we 
don't require dominance.

may_trap_p unfortunately returns false for PIC references in cases where 
they can clearly trap (as seen with the reduced testcase for this BZ in 
PIC mode).  I'm not really up for pulling on that thread right now.

Instead we just drop the may_trap_p exception and always verify 
dominance.  This fixes 79286 when generating PIC (and thus ought to fix 
the i686 darwin issues.

Bootstrapped and regression tested on i686-pc-linux-gnu.  Also hand 
verified the reduced testcase works with PIC.

Installing on the trunk.

Jeff