FpDebugger (pure): The dx-register is used to obtain the location of an exception. Fix for the difference in the dwarf-index of the dx-register on i386 and x86_64.

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@45429 4005530d-fff6-0310-9dd1-cebe43e6787f