I checked exhaustively today and found that the only characters (even
in Unicode) that Windows's default argv splitter will recognise as
word separators are the space and tab characters. So I think it's a
mistake to use <ctype.h> functions to identify word separators; we
should use that fixed character pair, and then we know we're getting
the right ones only.
(cherry picked from commit 9adfa797677ba5cc5a5c9db45e593a9e4ab293aa)
bdf7f73d3d