Arc: Remove obsolete targets

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
Arc: Fix target definitions for Windows

Make sure that target definitions will work properly on Windows by
dynamically checking for target OS name and using path relative to current
script in this case.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>