FpDbg: Read register-information on Darwin

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@44442 4005530d-fff6-0310-9dd1-cebe43e6787f
FpDbg: Use generic way to get value of instruction pointer register

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@44443 4005530d-fff6-0310-9dd1-cebe43e6787f