Update STD*_FILENO constants in settings.js to match unistd.h

They are 1,2,3 in unistd.h (correct) but were 0,1,2 in settings.js, so calling
`cDefine('STDOUT_FILENO')` (for example) would return the incorrect value.

This addresses issue #1570, but not #1408.
Merge pull request #1572 from rharkeadsk/fix-stdio-fileno-constants

Fix STD*_FILENO constants in JavaScript to match C