cmake: scripts: add 'winpty' support when available

Some Python scripts need to access to the underlying OS, like
using redirections. These interactions go through TTY interface.
On MinGW, these interactions/interfaces are called 'winpty'.
=> use them when available (harmless on platform *NIX platforms)

Signed-off-by: Cedric Lescop <cedric.lescop@se.com>