* fix breakage after writestr changes in r23888

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@24773 3ad0048d-3df7-0310-abae-a5850022a9f2
+ implemented dos.exec on i8086-msdos

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@24774 3ad0048d-3df7-0310-abae-a5850022a9f2