[compiler] Properly validate stable map assumption for globals.
For global object property cells, we did not check that the map on the
previous object is still the same for which we actually optimized. So
the optimized code was not in sync with the actual state of the property
cell. When loading from such a global object property cell, Crankshaft
optimizes away any map checks (based on the stable map assumption),
leading to arbitrary memory access in the worst case.
TurboFan has the same bug for stores, but is safe on loads because we
do appropriate map checks there. However mixing TurboFan and Crankshaft
still exposes the bug.