libstdc++/5625: exception unwinding creates invalid pointer o n mips

[cgd@broadcom.com]

FYI, I just checked in a change to the mips64 gdb simulator code so
that it will do checking of values (for many, but certainly not all
8-) which are allowed to produce UNPREDICTABLE results.

This causes 27 gcc (g++, actually) tests which previously passed to
fail, due to UNPREDICTABLE behaviour:

FAIL: g++.dg/eh/registers1.C execution test
FAIL: g++.dg/eh/unexpected1.C execution test
FAIL: g++.brendan/eh1.C  Execution test
FAIL: g++.eh/flow1.C  Execution test
FAIL: g++.eh/fntry1.C  Execution test
FAIL: g++.eh/ia64-1.C  Execution test
FAIL: g++.eh/inline2.C  Execution test
FAIL: g++.eh/pdel2.C  Execution test
FAIL: g++.eh/spec2.C  Execution test
FAIL: g++.eh/spec3.C  Execution test
FAIL: g++.eh/spec4.C  Execution test
FAIL: g++.eh/tmpl1.C  Execution test
FAIL: g++.mike/eh16.C  Execution test
FAIL: g++.mike/eh17.C  Execution test
FAIL: g++.mike/eh33.C  Execution test
FAIL: g++.mike/eh39.C  Execution test
FAIL: g++.mike/eh40.C  Execution test
FAIL: g++.mike/eh49.C  Execution test
FAIL: g++.mike/eh50.C  Execution test
FAIL: g++.mike/eh51.C  Execution test
FAIL: g++.mike/eh6.C  Execution test
FAIL: g++.other/eh3.C  Execution test
FAIL: g++.other/singleton.C  Execution test
FAIL: g++.other/vbase2.C  Execution test
FAIL: g++.pt/fntry1.C  Execution test
FAIL: g++.robertl/eb66.C  Execution test
FAIL: g++.robertl/eb88.C  Execution test



chris