[sgen] Fix 64-bit bug occurring when LOS object crosses cardtable overlap boundary.
[sgen] Use unified cardtable-update code in M&S, too.

The bug where objects crossed the cardtable overlap boundary cannot
happen with M&S because blocks are naturally aligned.  It can't hurt
to use the same code for updating them, too, though.
Merge remote-tracking branch 'origin/fix-los-cardtable-overlap'