cl: support alternative correct output(s) + fix nextafter on FTZ
In some situations, OpenCL program can return two or more different outputs, which are all correct by specification.
This will be used by follow-up nextafter fix.
Why it does look this ugly? Because no-one expected two different outputs will be desirable, so it's not that pretty.
Signed-off-by: David Heidelberg david@ixit.cz