Pushed changes introduced by LUKE (Johny B on the QB64 forums) as follows :
Fixed setup_lnx.sh, added _CWD$, fixed handling of errno.
Converted setup_lnx.sh to Linux line endings (was preventing the script from running).
We now include <errno.h>, so the errno variable actually works - before it was just a regular variable that wasn't being set on error.
Added a _CWD$ function that returns the current working directory. Should work on all 3 systems, but testing is needed on Win/Mac.
Can cause the following runtime errors: 7 (Out of memory), 51 (Internal error).
