runtime/qio: use getcwd instead of getwd

getwd is deprecated in favor of getcwd.

Related to #325.
I managed to get it using Python, I generate a .stdin file in the .preexec file, not sure if this is a good practice. I don't know whether it's good to using Python in the .preexec file.

For some reason, it's reporting "No such file or directory", so it's like getcwd is returning ENOENT.

Looking at getcwd's man page, I can see that ERANGE is returned only when the size is greater than zero but smaller than the length of the pathname plus 1, but it's possible that it doesn't hold for the case where size is MAXPATHLEN.

According to the same man page, ENOENT is returned when "a component of the pathname no longer exists", which doesn't make sense.

I will send the changes for review (not for merging, yet), so you can have a look at the code.